Sheet-shaped stretchable structure, and resin composition for stretchable resin sheet and stretchable resin sheet used for the structure

ABSTRACT

A sheet-shaped stretchable structure including stretchable resin sheets laminated together is provided. A conductive layer may be disposed at least at one of several positions. For example, the conductive layer may be disposed between any two adjacent ones of the laminated stretchable resin sheets. The conductive layer may be disposed on a top surface of an uppermost one of the laminated stretchable resin sheets. Further, the conductive layer may be disposed on a bottom surface of a lowermost one of the laminated stretchable resin sheets, and a via hole.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.14/944,338, filed Nov. 18, 2015, which claims the benefit of JapanesePatent Application No. 2014-239899, filed Nov. 27, 2014, and JapanesePatent Application No. 2015-076692, filed Apr. 3, 2015. The entiredisclosure of each of the above-identified applications, including thespecification, drawings, and claims, is incorporated herein by referencein its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a stretchable resin sheet and asheet-shaped stretchable structure with a high level of tensile stressrelaxation properties and excellent restoration properties afterextension. The disclosure also relates to the resin composition used forthe stretchable resin sheet and the sheet-shaped stretchable structure.

2. Background Art

In the field of electronics, particularly in various interfaces such assensors, displays, and artificial skins for robots, there is anincreasing need to improve wearability and shape-fitting properties.More specifically, there is a growing demand for devices that areflexible and deformable to be placed on curved or uneven surfaces. Tomeet this demand, stretchable electronic devices have been developed andexpected as a future electronics technology.

To make an electronic device freely deformable, however, not only theelectronic circuit board needs to be stretchable, but also electroniccomponents mounted on the board need to be resistant to deformationstress. Therefore, it has been attempted to make semiconductorsthemselves stretchable (for example, Unexamined Japanese PatentPublication No. 2014-17495).

Meanwhile, flexible display devices such as electronic papers have beendeveloped using flexible resin materials. Electronic papers, which comein various types such as electrophoretic and twist ball types, aregenerally formed of two laminated layers: a display layer to achieve adisplay and a conductive layer to which a voltage is applied.Electrophoretic flexible display devices usually employ urethane resin(for example, Unexamined Japanese Patent Publication No. 2012-63437),whereas twist ball display devices usually employ silicone resin (forexample, Unexamined Japanese Patent Publication No. 2012-27488).

SUMMARY

The present disclosure provides a flexible, stretchable sheet-shapedstructure.

The sheet-shaped stretchable structure used as an electronics elementaccording to an aspect of the present disclosure has a stretch of notless than 10% and includes a plurality of laminated stretchable resinsheets. At least one hollow is provided between at least one of pairs oftwo adjacent ones of the laminated stretchable resin sheets.

Providing the hollow satisfies not only mountability and sealingproperties, but also extensibility, allowing the structure to beflexible and pliable. In addition, using this structure can provideflexible display devices, electronic circuits, etc. that can fit anycurved surface and accommodate themselves to large deformation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a sheet-shaped stretchable structure(electronic paper) according to a first exemplary embodiment of thepresent disclosure.

FIG. 2 is a schematic view of the procedure for manufacturing astretchable resin sheet used in the sheet-shaped stretchable structureshown in FIG. 1.

FIG. 3 is a sectional view of another sheet-shaped stretchable structureaccording to the first exemplary embodiment of the present disclosure.

FIG. 4 is a sectional view of a stretchable resin sheet used in thesheet-shaped stretchable structure shown in FIG. 3.

FIG. 5 is a perspective view of the stretchable resin sheet shown inFIG. 4.

FIG. 6 shows the procedure for manufacturing a stretchable electroniccircuit member including an electronic component according to the firstexemplary embodiment of the present disclosure.

FIG. 7 is a sectional view of further another sheet-shaped stretchablestructure according to the first exemplary embodiment of the presentdisclosure.

FIG. 8 is a sectional view of a stretchable resin sheet used in thesheet-shaped stretchable structure shown in FIG. 7.

FIG. 9 is a perspective view of the stretchable resin sheet shown inFIG. 8.

FIG. 10 is a sectional view of a stretchable structure with hollowsaccording to the first exemplary embodiment of the present disclosure,which is composed of a flat stretchable resin sheet and support members(formed by photolithography).

FIG. 11 is a sectional view of further another sheet-shaped stretchablestructure according to the first exemplary embodiment of the presentdisclosure.

FIG. 12 is a perspective view of a stretchable resin sheet used in thesheet-shaped stretchable structure shown in FIG. 11.

FIG. 13A shows a photo showing the results of display propertiesevaluated in Example 4 according to the first exemplary embodiment ofthe present disclosure.

FIG. 13B shows a photo showing the stretchable structure shown in FIG.13A When a polarity-reversed voltage is applied.

FIG. 14 is a graph showing the behavior of an extension-restoration testapplied to the stretchable resin sheet of a second exemplary embodimentof the present disclosure and other stretchable resin sheets used forcomparison.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Exemplary Embodiment

Prior to describing a first exemplary embodiment of the presentdisclosure, problems associated with the conventional techniques willnow be briefly described.

A semiconductor with a corrugated shape as in Unexamined Japanese PatentPublication No. 2014-17495 is limited in stretchability and difficult tobe processed. Moreover, this technique cannot be applied to othermounted components than semiconductors. Therefore, it is required thatthe device architecture be designed so that unstretchable mountedcomponents can be prevented from being subjected to stress due tostretching deformation.

The device architecture requires properties such as the ease ofworkability and installation according to different scenes. For example,thermoplastic resin films of polyethylene terephthalate (PET),polyimide, and polyethylene naphthalate (PEN) can be bent but cannot bestretched. Therefore, they are not adaptable to movable or stretchyparts such as the flexible joints of the body. The device architecturefurther requires stretchability and pliability because otherwisecircuits and elements disposed inside or outside the device would bebroken when a curved surface like a sphere is formed by molding underhigh heat and pressure.

In Unexamined Japanese Patent Publication No. 2014-17495, the wrinklingprocess allows stretching in a single-axial direction, but not inmulti-axial directions. Moreover, the stretchable region depends on theshape of the wrinkles, and can be broken when stretched beyond themaximum length of the stretchable region.

Therefore, elements manufactured by the wrinkling process are easilyexfoliated or broken due to unexpected deformation. For this reason,current flexible display devices are not more than slightly bendable.

Structures in electronics have so far been widely studied to improvetheir flexibility, but it has rarely been reported to successfully makethe structures stretchable. The reason for this seems to be as follows.Not only the material for the structures, but also the substrate onwhich elements and components are to be mounted are lack ofstretchability, and substrates made of stretchable material cannoteasily mount elements and components thereon.

Hereinafter, the first exemplary embodiment of the present disclosurewill now be described, but the present disclosure is not limited to thisembodiment.

First, a sheet-shaped stretchable structure according to the firstexemplary embodiment of the present disclosure will be described. FIG. 1is a sectional view of the sheet-shaped stretchable structure(hereinafter, the structure) of the present exemplary embodiment. Thestructure includes a plurality of laminated stretchable resin sheets(hereinafter, sheets) 2A and 2F, and hollows 7 are provided betweensheets 2A and 2F. In short, the structure is made of only stretchablematerials and has hollows 7 therein. This configuration allows thestructure to have a stretch of not less than 10%. As a result, thestructure has excellent stretchability and mountability and also canseal a liquid and elements inside it. In the example shown in FIG. 1,hollows 7 are filled with electrophoretic liquid 5, such as pigment, andsealed. This structure is used as an electronics element. In thefollowing description, sheets 2A and 2F, the materials used to formthese sheets, and other sheets 2B to 2E described later may becollectively referred to as sheets 2.

In the present exemplary embodiment, the term “excellent stretchability”means to be elastically deformable, extensible, plasticallyundeformable, and to have few residual strains after deformation. Morespecifically, it means to have an extension of not less than 10% andalmost no plastic deformation.

The shape and production method of hollows 7 are not limited; forexample, hollows 7 can be formed as shown in FIG. 2. FIG. 2 is aschematic view of the procedure of manufacturing sheet 2A, which has anuneven surface. This shape can be preferably formed by embossing thesurface of stretchable resin Embossing the surface to form a raised orrecessed pattern allows hollows 7 to be formed by a smaller number ofprocesses. In FIG. 2, sheet 2 is disposed between mold 3 with raisedportions arranged at certain intervals and flat metal plate 1, and thenembossed under heat and pressure by pressing flat metal plate 1 fromabove. Sheet 2A may alternatively be formed by coating uncured resin onmold 3 and curing it or by coating moldable resin on mold 3 and dryingit.

Sheet 2A obtained in this manner is bonded to sheet 2F so as to formseparate hollows 7. Sheets 2A and 2F bonded together are then sandwichedbetween transparent electrodes 6. The obtained structure can be used asan electronic paper.

Alternatively, hollows 7 can be formed by using an unillustrated moldwith a recessed pattern. Still alternatively, it is possible to emboss aflat film by laser drilling. Besides these methods, conventional andimproved methods can be used.

The structure of the present exemplary embodiment preferably has astretch of 10% to 500%, and more preferably 30% to 300%. A structurewith a high extension of not less than 10% has high shape-fittingproperties and is not easily broken, allowing hollows 7 to be kept asspaces while being extended. In contrast, a structure with a stretch ofless than 10% is unpreferable because it can easily be broken whendeformed. A structure composed of both a material with a stretch of notless than 10% and a material with a stretch of less than 10% is alsounpreferable because the material with the extension of less than 10%can be broken and induce the breakage of the structure.

The structure does not need to have an upper limit of extension;however, in order to approximately maintain the height and volume ofhollows 7, it is preferable that the stretch is not more than 500%.

As long as satisfying the above-described properties, the structure ofthe present exemplary embodiment may contain any material, butpreferably contains a resin sheet with a stretch of not less than 10%.

Preferable examples of the resin composition for stretchable resin sheetthat can be used in the present exemplary embodiment include thefollowing: silicone resin, urethane resin, various rubbers, andthermosetting resin. Among them, thermosetting resin is preferablebecause sheets 2A and 2F, when made of thermosetting resin, can beexcellent in heat resistance and adhesion between them. Thethermosetting resin can be combined with filler to provide features suchas low-thermal expansion, elasticity control, thermal conductivity,light reflectivity, and electrical conductivity.

Examples of the thermosetting resin include the following: epoxy resin,phenol resin, polyimide resin, urea resin, melamine resin, andunsaturated polyester. Among them, epoxy resin is preferable.

Examples of the epoxy resin include the following: bisphenol A epoxyresin, bisphenol F epoxy resin, bisphenol S epoxy resin, aralkyl epoxyresin, phenol novolac epoxy resin, alkyl phenol novolac epoxy resin,biphenol epoxy resin, naphthalene epoxy resin, dicyclopentadiene epoxyresin, an epoxy compound of a condensation product of a phenol and anaromatic aldehyde with a phenolic hydroxyl group, triglycidylisocyanurate, and alicyclic epoxy resin. They may be used alone or incombination of two or more thereof depending on the situation.

The epoxy resin more preferably has two or more epoxy groups and threemethyl groups per molecule and has a molecular weight of not less than500. The epoxy resin can be any commercially available one such asfollows: jER1003 (available from Mitsubishi Chemical Corporation, whichis bifunctional and has 7 to 8 methyl groups and a molecular weight of1300); EXA-4816 (available from DIC corporation, which is bifunctionaland has a molecular weight of 824 and many methyl groups); and YP50(available from Nippon Steel & Sumikin Chemical Co., Ltd., which isbifunctional and has molecular weight of 60000 to 80000 and many methylgroups).

The above-enumerated epoxy resins may be used alone or in combination oftwo or more thereof.

It is preferable that at least one of sheets 2A and 2F be transparent.This ensures a large field of view, thereby not only facilitating thelocalization of the mounted components, but also providing the displayfunction.

Some applications allow at least one of sheets 2A and 2F to be opaque.In the present exemplary embodiment, an opaque sheet is obtained byadding filler such as particles to the resin composition for stretchableresin sheet. The term “filler” here means one which is used to improveelectrical and thermal conductivity or to reduce thermal expansion. Whenused for display applications, the filler can be particles used toimprove reflectance and hence visibility, thereby improving a contrast.

Using filler allows controlling not only the resin strength and thethermal expansion coefficient, but also water-absorbing properties andelectroconductivity.

The filler can be of various types depending on the application. It ispreferable that the filler includes at least one selected from organicfibers, carbon fibers, glass fibers, and metal fibers. Using such fillerreinforces the resin strength, allowing the stretchable resin sheet tobe pliable and tough. Using such filler also facilitates the control ofthe linear thermal expansion, making the stretchable resin sheet easierto deal with, more electrically conductive and less expensive. Ifneeded, these fibers can be surface-treated with a coupling agent orsurface-modified by graft polymerization by any of conventional andimproved methods. The fiber fabrics can be of any type such as woven andnonwoven.

Examples of the organic fibers include the fibers based on the followingmaterial: polyethylene, poly(p-phenylenebenzobisoxazole), aramid,polyester, vinylon, polypropylene, nylon, rayon, polylactic acid,polyarylate, polyphenylene sulfide, polyimide, and fluorine resin.

Examples of the metal fibers include fiber fabrics of steel and silver,and random mesh.

Other examples of the filler can be selected from spherical, crushed,flaky, and discontinuous fiber-like particles. The components of thefiller are not particularly limited and may, for example, contain atleast one substance including an element selected from Si, Cu, Ag, Au,Al, Mg, Pt, and Ti. Using such filler reduces the cost and improves thelinear expansion, electrical conductivity, flame retardance, and opticalproperties such as refractive index. The size and particle diameter ofthe filler are not particularly limited; however, when the particlediameter is in the range from 1 nm to 100 nm, the filler can be used incomparatively small amounts to effectively improve the opticalproperties, electrical conductivity, and linear expansion. Meanwhile,fillers with a particle diameter in the range from 100 nm to 50micrometers are cost advantageous as material and easy to deal with andcost advantageous for manufacture.

Specific examples of the substance including the element selected fromSi, Cu, Ag, Au, Al, Mg, Pt, and Ti include the following particles,flakes, and wires: silica, copper particles, copper-plated particles,silver particles, silver flakes, silver wires, silver-plated particles,gold particles, gold wires, gold-plated particles, aluminum particles,aluminum oxide particles, aluminum hydroxide particles, magnesiumparticles, magnesium hydroxide, magnesium oxide, platinum particles,platinum-plated particles, titanium particles, titanium oxide particles,and titanium oxide-coated particles. They may be used alone or incombination of two or more thereof. These particles, flakes, and wiresmay be used according to any of conventional and improved methods. Morespecifically, filler can be added to a varnish made by dissolving resinin a solvent and dispersed using a dispersing machine such as a beadmill, a jet mill, a planetary stirrer, a homodisper, or an ultrasonicwave disperser.

Still other examples of the filler include carbon nanotubes and/or metalwires. Using such filler is preferable to efficiently provide the resincomposition with electrical conductivity. More specifically, the samelevel of electrical conductivity can be provided by adding smalleramounts of filler than spherical and flaky conductive materials. Thus,such filler is preferable because of its high cost-effectiveness as wellas its easiness to maintain resin properties, allowing the resincomposition to maintain its electrical conductivity when stretched,bent, or deformed in other ways.

These conductive materials can be dispersed in resin by any ofconventional and improved methods. More specifically, dispersion liquidis prepared by adding filler and a dispersant such as a cellulosic oramine- or sulfuric acid-based ionic liquid to a solvent such as water,methyl isobutyl ketone, methyl ethyl ketone, toluene, acetone, ordimethylformamide. Next, resin is added to the dispersion liquid, andthe solvent is removed to disperse the filler into the resin.

The carbon nanotube is not particularly limited in type, but can be, forexample, a single-wall carbon nanotube, a double-wall carbon nanotube,or a multiwall carbon nanotube. These carbon nanotubes can bysynthesized by any of conventional and improved methods. Different typesof carbon nanotubes are used for different purposes; for example, inorder to give priority to electrical conductivity, it is preferable touse a carbon nanotube with high crystallinity, that is, a G/D ratio of10 or more when determined by Raman spectroscopy.

Examples of the metal wire include discontinuous metal fibers with highaspect ratio, such as silver nanowires, silver nanorods, and goldnanorods.

The sizes of these carbon nanotubes and metal wires are not particularlylimited; however, when the diameter is not less than 1 nm and not morethan 100 nm and the length is not less than 1 micrometer and not morethan 10 mm, the filler can be well dispersed in the resin so as toimprove electrical conductivity and reinforcement.

The above-enumerated fillers may be used alone or in combination of twoor more thereof.

In the case that the resin composition contains filler, the fillercontent can be properly adjusted according to the use of the stretchableresin sheet; it is preferably not less than 0.05 wt % and not more than80 wt %, in general. In this range, the resin properties can bemaintained, and appropriate functions can be provided.

A filler content of less than 0.05 wt % is not preferable because it maynot allow taking advantage of filler properties such as low-thermalexpansion, thermal conductivity, and electrical conductivity. A fillercontent of more than 80 wt % is not preferable because it may not allowtaking advantage of resin properties such as stretchability, pliability,and extensibility.

The filler content of not less than 0.05 wt % and not more than 50 wt %is considered to be more preferable because it provides high stressrelaxation properties and few residual strains.

In the present exemplary embodiment, all of sheets 2 can be made ofeither the same or different types of materials (resins).

In a preferred exemplary embodiment, one of sheets 2 can be used as thebase member, and the other can be used as a sealing member, andafter-mentioned various members and/or materials can he sealed inhollows 7 formed between the base member and the sealing member. Thisenables the stretchable structure of the present exemplary embodiment tobe used as an electronics element for many purposes.

In the present exemplary embodiment, hollows 7 means separate spacesformed between at least one of pairs of two adjacent ones of two or morelaminated sheets 2 inside the stretchable structure.

In the case of using three or more laminated sheets 2, hollows 7 do notnecessarily have to be formed between each adjacent pair; hollows 7 haveonly to be formed between at least one pair. For example, hollow 7 hasonly to be formed at least between the base member and the seatingmember, and either a base member or a sealing member may be composed oftwo or more laminated sheets 2.

In the stretchable structure of the present exemplary embodiment,hollows 7 may have any shape and space occupancy as long as thestructure satisfies the above condition. For example, for the purpose ofsealing electronic components, the space occupancy of hollow(s) 7 is 1%to 50% of the stretchable structure. For the purpose of sealing a liquidused for the display, the space occupancy is preferably not less than50%.

In a structure including two laminated sheets 2, hollow 7 can be formedby providing an adhesive layer between the surface of the base memberformed of one sheet 2 and the surface of the sealing member formed ofthe other sheet 2 facing the base member surface. The adhesive layer maybe formed on the surface of either the base member or the sealingmember. Providing the adhesive layer facilitates bonding the base memberand the sealing member.

The adhesive layer may have any thickness and may be made of anymaterial, such as curing resin or adhesive resin. Examples of the curingresin that can be used for the adhesive layer include the following:acrylic resin, epoxy resin, urethane resin, and silicone resin. Examplesof the adhesive resin include terpene-based resin and unsaturatedaliphatic resin in addition to the above-mentioned resins.

Modified examples of hollows 7 will now be described with reference toFIGS. 3 to 5. FIG. 3 is a sectional view of another sheet-shapedstretchable structure of the present exemplary embodiment. FIG. 4 is asectional view of stretchable resin sheet (hereinafter, sheet) 2B usedin the sheet-shaped stretchable structure shown in FIG. 3. FIG. 5 is aperspective view of sheet 2B. The structure shown in FIG. 3 has hollow 7formed by combining sheet 2B with a recessed pattern and flat sheet 2F.

A procedure of sealing LED 10 as an electronic component into hollow 7of a structure similar to the structure shown in FIG. 3 will now bedescribed with reference to FIG. 6.

First, in the same manner as in FIG. 3, sheet 2E with a recessed patternand flat sheet 2F are prepared. Meanwhile, stretchable conductive pasteis prepared and formed into wires 9A and lands 9B on the surface ofsheet 2E. Lands 9B function as connections between the printed wires andthe LED. The stretchable conductive paste is prepared by, for example,adding 90 wt % of silver particles with a diameter of 2.1 micrometers tourethane resin (HUX-561 available from Adeka Corporation). Next, LED 10as an electronic component is installed in hollow 7 and is connected tolands 9B using an electrically conductive adhesive.

Next, sheets 2F and 2E are bonded together and LED 10 is sealed withinhollow 7 by, for example, heating at 170 degrees Celsius for one hour.Finally, for being connecting LED 10 to an external power supply, afterthe sheets are laser-drilled, vias 12 and wires 9A are printed using theabove-described stretchable conductive paste and then connected to thepower supply.

As another modified example, as shown in FIG. 7, hollow 7 can be formedby combining stretchable resin sheet (hereinafter, sheet) 2C with araised pattern. with flat sheet 2F. FIG. 7 is a sectional view offurther another sheet-shaped stretchable structure of the presentexemplary embodiment. FIGS. 8 and 9 are a sectional view and aperspective view, respectively, of sheet 2C with projections 8A.Projections 8A function as support members to keep the height of hollow7. This structure allows maintaining hollow 7 stably.

Projections 8A can be formed, for example, by regularly or irregularlyembossing at least one of the base member and sealing member which aresheets 2 (2F).

As shown in FIG. 10, it is possible to replace sheet 2C by flat sheet2F, to provide columnar bodies 8B on the surface of flat sheet 2F, andto combine sheet 2C with another sheet 2F. FIG. 10 is a sectional viewof a stretchable structure of to the present exemplary embodiment formedby combining flat sheets 2F and columnar bodies 8B as the supportmembers. Columnar bodies 8B can be formed on sheet 2F, for example, byphotolithography.

As shown in FIGS. 11 and 12, columnar bodies 8B may be replaced by beads8C, which are formed on fiat sheet 2F. FIG. 11 is a sectional view offurther another sheet-shaped stretchable structure of the presentexemplary embodiment. FIG. 12 is a perspective view of stretchable resinsheet (hereinafter, sheet) 2D used in the sheet-shaped stretchablestructure shown in FIG. 11. Beads 8C function in the same manner ascolumnar bodies 8B. Hollow 7 can be formed by disposing sheet 2D in sucha manner that beads 8C, which function as spacers, are disposed betweenthe base member and the sealing member. Although not illustrated,columnar bodies 8B and beads 8C can be replaced by a mesh-sheet spacer.

Projections 8A, columnar bodies 8B, and beads 8C are not limited inshape, height and the area ratio in plane. For example, in the case ofsealing a liquid crystal within hollow 7, a height of not more than 10micrometers is preferable for visibility and cost reasons. Meanwhile, inthe case of sealing film-like electronic components or elements withinhollow 7, it is preferable to determine the height of hollows 7according to the height of the electronic components or elements so asto give first priority to their protection.

The method of manufacturing the stretchable resin sheet of the presentexemplary embodiment is not particularly limited. For example, in thecase of using one of the above-enumerated epoxy resins as well assilicone resin or urethane resin, a resin-containing solution such as anemulsion, or a resin composition is first prepared using a curing agentor a solvent if necessary.

The resin composition thus prepared is coated to have a desiredthickness on a release-treated film using a bar coater or a spin coater.Next, the solvent is removed by heat-drying and the resultant is curedwith heat or light, thereby forming a stretchable resin sheet.

The resin composition may be heat-dried and cured using any of theconventional and improved methods, devices, and conditions.

The specific temperature and time of the heating can be properlyadjusted according to the used cross-linking agent, solvent, and thelike. For example, the resin composition can be obtained by drying orcuring for 30 to 180 minutes at 130 to 200 degrees Celsius, which is notlower than either the boiling point of the solvent or the glasstransition point.

Alternatively, the resin composition can be semi-cured by adjusting thetemperature and time of drying or curing. Semi-cured sheet 2 can bedisposed between two adjacent sheets 2 so as to function as an adhesiveto bond them. An additional curing process can be performed tocompletely integrate these sheets. Semi-cured sheet 2 can alternativelybe used outside the adjacent sheets in order to bond the sealing memberand the base member together.

Sheets 2 can also be bonded together using an adhesive as describedabove. The adhesive can be any type, such as acrylic resin, epoxy resin,urethane resin, silicone resin, terpene-based resin, and unsaturatedaliphatic resin. These adhesives can be coated on a release-treatedsheet using a bar coater or a spin coater, and then transferred to sheet2 to be bonded, thereby forming an adhesive layer. Another method ofbonding sheets 2 together is to bond the adhesive layer directly to thestretchable resin sheet by the above-described method. In the presentexemplary embodiment, not only this conventional method but also otherimproved methods can be used.

Two or more laminated sheets 2 are bonded together by theabove-described method or other methods, thereby forming hollow 7, andhence, the stretchable structure. If necessary, it is also possible toprovide an insertion opening such that hollow 7 is communicated with theoutside of the stretchable structure.

An insertion opening is preferable, for example, to introduce a liquidor elements into hollow 7. After hollows 7 are formed by bondinglaminated sheets 2 together, a desired liquid can be introduced intoarbitrary hollow 7 through the insertion opening by a dispenser or by amethod such as vacuum differential pressure casting, immersion, directcompressing, and centrifugal compressing.

In the case of the absence of an insertion opening, a liquid is appliedto either flat sheet 2F or embossed sheet 2B or 2C. In order to seal anelectronic component, sheet 2E on which the electronic component ispreviously mounted is bonded to another sheet 2 as described withreference to FIG. 6. Sealing an electronic component within hollow 7 canincrease the range of packaging options and the size of the electroniccomponent, thereby greatly reducing design constraints. The liquid andthe electronic component can be introduced and sealed into hollow 7 byany of the conventional and improved methods.

As described with reference to FIG. 6, in order to form a circuit orelectrodes, it is preferable to provide a conductive layer at one of thefollowing positions: between any adjacent ones of sheets 2; on the topsurface of the uppermost one of sheets 2, and on the bottom surface ofthe lowermost one of sheets 2 used in the structure of the presentexemplary embodiment. The conductive layer allows the connection betweenhollows 7 and a device. The conductive layer is preferably resistant tostretching, and can be formed by any of the conventional and improvedmethods.

More specifically, the conductive layer can be formed by applyingprinting, coating, or etching technique to the following materials:copper foil in the shape of a horseshoe, a rectangle, a zigzag pattern,or a waveform; silver paste; silver nanowire; carbon nanotube; orconductive polymer. Any other material resistant to stretching can beused alone or in combination to form the conductive layer.

The above-mentioned conductive layer can alternatively be formed bycoating or deposition, and then, insulation space can be drawn by alaser so as to form a circuit. It is also possible to a circuit patternby exposure and development after forming a resist layer on sheet 2 byphotolithography or lifting up. It is also possible to directly form acircuit pattern on sheet 2 using a laser by a semi-additive process,followed by applying electroless plating. It is also possible to employa printing method using a gravure plating plate or a screen platingplate, or a conductive ink-jet printing. The circuit pattern canincrease the design freedom of electronic devices, such as wearableterminals.

Further, as the circuit structure, it is possible to form a through-holepassing through sheet 2 and connecting the electronic component inhollow 7 with a device. A via hole for connecting both sides of sheet 2as a circuit wiring may be formed. A hole for mounting a connector maybe formed. It is also possible to form a land or pad for mounting andsoldering an electronic component, or a wire connecting the land and thepad. The conductive layer can be formed on one or both sides of sheet 2.In the case that two or more of the same type of sheets 2 are bondedtogether, three or more conductive layers can be formed.

The stretchable structure of the present exemplary embodiment can beused as an electronics element for various applications. For example, inthe case that a conductive layer is provided and that a liquid orpigment required for display such as a cholesteric liquid crystal or anelectrophoretic solution is introduced within hollow 7, the structurecan be used as a stretchable electronic paper. In addition, constraintson the installation location of the display can be greatly reduced.

Cholesteric liquid crystals are display materials that are liquid at oraround room temperature and become visible when the orientation in themolecular structure is changed by a potential difference.Electrophoretic solutions are used as display materials and containpositively and negatively charged pigment particles of different colorsdispersed therein.

Electrophoretic solutions can be prepared by adding positively chargedblack particles, negatively charged white particles, a dispersant, and acharge control agent, to a high-boiling-point solvent, and dispersingthem ultrasonically. Using such an electrophoretic solution allows thepigment particles to be drawn to opposite electrodes by the potentialdifference, thereby achieving a mechanism for producing visibility.Other materials and mechanisms designed for display can be used by anyof the conventional and improved methods.

As another aspect of the present embodiment, an electronic component oran element may be installed in hollow 7 of the stretchable structure.The position and the method of installation of the electronic componentor the element is not particularly limited; it is possible to use anadhesive, a double-sided adhesive tape, paste, solder, etc. that areelectrically conductive. It is also possible to seal the electroniccomponent, the element or the wiring part together with a shieldingmaterial so as to improve moisture- and oxygen-shielding properties.Although the material used for sealing can be either stretchable or not,the proportion of the volume of the sealed electronic component or theelement (the target object) with respect to the total volume ofhollow(s) 7 in the entire structure is preferably not more than 50%, andmore preferably not more than 20%. In this range, the stretchability ofthe structure can be preferably maintained.

Effects of the present exemplary embodiment will now be described inspecific examples, but the present disclosure is not limited to theseexamples.

EXAMPLES Example 1 Production (I) of a Sheet-Shaped StretchableStructure with Hollows 7

(Example 1-1)

First, the following materials are uniformly mixed: 75 parts by weightof epoxy resin (jER1003 available from Mitsubishi Chemical Corporation);100 parts by weight of polyrotaxane (SH3400P available from AdvancedSoftmaterials Inc.); 45 parts by weight of cross-linking agent(isocyanate, DN-950 available from DIC corporation); and 1.1 parts byweight of imidazole-based curing accelerator (2-ethyl-4-methylimidazole,2E4MZ available from Shikoku Chemicals Corporation). The obtainedmixture is heated at 100 degrees Celsius for 10 minutes, thereby formingtwo stretchable resin sheets 2 each with a thickness of 50 micrometers.One of sheets 2 is formed into stretchable resin sheet 2B with arecessed pattern by molding it in a mold with a raised pattern, and theother is directly used as flat stretchable resin sheet 2F. Next, sheets2B and 2F are bonded together and heated at 170 degrees Celsius for onehour, thereby forming a sheet-shaped stretchable structure with hollows7 (extension: 130%) (see FIGS. 3 to 5).

(Example 1-2)

First, the following materials are uniformly mixed: 100 parts by weightof silicone elastomer (Silpot 184 available from Dow Corning Toray Co.,Ltd.); and 10 parts by weight of silicone resin catalyst (silpot184 CATavailable from Dow Corning Toray Co., Ltd.). The obtained resin mixtureis heated at 100 degrees Celsius for 5 minutes, thereby forming onestretchable resin sheet 2 (2F) with a thickness of 50 micrometers. Inaddition, the same resin mixture is coated on the same mold with araised pattern as used in Example 1-1, heated at 100 degrees Celsius forone hour, and removed from the mold, thereby forming sheet 2B with arecessed pattern. Next, sheets 2B and 2F are bonded together and heatedat 100 degrees Celsius for one hour, thereby forming a sheet-shapedstretchable structure with hollows 7 (extension: 160%).

(Example 1-3)

First, sheet 2B with a recessed pattern is formed as follows: 100 partsby weight of urethane resin (MIX-561 available from Adeka Corporation)is coated on a mold with a raised pattern in the same manner as inExample 1-2, heated at 100 degrees Celsius for one hour, and removedfrom the mold. Next, HUX-561 is coated on a PET film (support body),laminated on top of sheet 2B in such a manner that the side with theraised pattern of sheet 2B faces the coated resin, and heated at 100degrees Celsius for one hour, thereby forming a sheet-shaped stretchablestructure with hollows 7 (extension: 400%).

(Example 1-4)

First, the following materials are uniformly mixed: 100 parts by weightof an ethylene oxide adduct of hydroxyphenyl fluorene epoxy resin(EG-280 available from Osaka Gas Chemicals Co., Ltd.); 45 parts byweight of cross-linking agent (isocyanate, DN-950 available from DICcorporation); 1.1 parts by weight of imidazole-based curing accelerator(2E4MZ available from Shikoku Chemicals Corporation); and 50 parts byweight of acid anhydride curing agent (YH306 available from MitsubishiChemical Corporation). Subsequently, the same procedure as in Example1-1 is performed, thereby forming a sheet-shaped stretchable structure(extension: 400%).

Example 2 Production (II) of a Sheet-Shaped Stretchable Structure withHollows 7

(Example 2-1)

The same two sheets 2 as used in Example 1-1 are prepared. One is formedinto embossed stretchable resin sheet 2C with a raised embossed patternby molding it in a mold with embossed cubes each having sides of 30micrometers (see FIGS. 8 and 9), and the other is directly used as flatsheet 2F. Next, sheets 2C and 2F are bonded together and heated at 170degrees Celsius for one hour, thereby forming a sheet-shaped stretchablestructure with hollow 7 (extension: 120%).

(Example 2-2)

First, the same components as used in Example 1-2 are uniformly mixedand heated at 100 degrees Celsius for 5 minutes, thereby forming onesheet 2F with a thickness of 50 micrometers. The resin mixture is alsocoated on the same embossed mold as used in Example 2-1, heated at 100degrees Celsius for one hour, and removed from the mold, thereby formingsheet 2C with a raised embossed pattern. Next, sheets 2C and 2F arebonded together and heated at 100 degrees Celsius for one hour, therebyforming a sheet-shaped stretchable structure with hollow 7 (extension;160%).

(Example 2-3)

First, the same components as used in Example 1-3 are uniformly mixed,coated on the same embossed mold same as in Example 2-2, heated at 100degrees Celsius for one hour, and removed from the mold, thereby formingsheet 2C with a raised embossed pattern. Next, HUX-561 is coated on aPET film (support body), laminated on top of sheet 2C in such a mannerthat the embossed side of sheet 2C faces the coated resin, and heated at100 degrees Celsius for one hour, thereby forming a sheet-shapedstretchable structure with hollow 7 (extension: 400%).

(Example 2-4)

First, the same components as used in Example 1-4 are uniformly mixed.Subsequently, the same procedure as in Example 2-1 is performed, therebyforming a sheet-shaped stretchable structure (extension: 400%).

Example 3 Production (III) of a Sheet-Shaped Stretchable Structure withHollow 7

(Example 3-1)

First, the same components as used in Example 1-1 are uniformly mixedand heated at 100 degrees Celsius for 10 minutes, thereby forming twosheets 2 (2F) each with a thickness of 50 micrometers. Next, beadsspacers with a diameter of 10 micrometers are sprayed and arranged atappropriate intervals on one of sheets 2 (2F) (see FIG. 12). The othersheet 2F is then laid on the first sheet 2F so that the beads spacersare sandwiched between two sheets 2F. The laminated sheets are thenheated at 170 degrees Celsius for one hour, thereby forming asheet-shaped stretchable structure with hollow 7 (extension: 150%).

(Example 3-2)

First, the same components as used in Example 1-2 are uniformly mixedand heated at 100 degrees Celsius for 5 minutes, thereby forming twosheets 2 (2F) each with a thickness of 50 micrometers. Next, beadsspacers with a diameter of 10 micrometers are sprayed and arranged atappropriate intervals on one of sheets 2F. The other sheet 2F is thenlaid on the first sheet 2F so that the beads spacers are sandwichedbetween two sheets 2F. The laminated sheets are then heated at 100degrees Celsius for one hour, thereby forming a sheet-shaped stretchablestructure with hollow 7 (extension: 200%).

(Example 3-3)

First, the same components as used in Example 1-3 are coated on a PETfilm (support body), and glass beads spacers with a diameter of 20micrometers are sprayed and arranged at appropriate intervals on thecoated matter. The film is then heated at 100 degrees Celsius for onehour, thereby forming stretchable resin sheet 2D whose surface isembedded with some of the glass beads spacers. Next, a PET film coatedwith HUX-561 and used as a base member is laid on the bead-sprayedsurface of sheet 2D. The resulting object is heated at 100 degreesCelsius for one hour, thereby forming a sheet-shaped stretchablestructure with hollow 7 (extension: 500%).

(Example 3-4)

First, the same components as used in Example 1-4 are uniformly mixed.Subsequently, the same procedure as in Example 3-1 is performed, therebyforming a sheet-shaped stretchable structure (extension: 500%).

(Example 3-5)

First, the following materials are uniformly mixed: 100 parts by weightof epoxy resin (jER1003 available from Mitsubishi Chemical Corporation);100 parts by weight of polyrotaxane (SH3400P available from AdvancedSoftmaterials Inc.); 45 parts by weight of cross-linking agent(isocyanate, DN-950 available from DIC corporation); 1.1 parts by weightof imidazole-based curing accelerator (2-ethyl-4-methylimidazole, 2E4MZavailable from Shikoku Chemicals Corporation); and glass filler(CF0111-B15C available from Nippon Frit Co., Ltd.). Subsequently, thesame procedure as in Example 1-1 is performed, thereby forming asheet-shaped stretchable structure (extension: 90%).

Comparative Examples

(Comparative Example 1-1)

First, the following materials are uniformly mixed: 100 parts by weightof epoxy resin (jER1003 available from Mitsubishi Chemical Corporation);and 5 parts by weight of imidazole-based curing accelerator(2-ethyl-4-methylimidazole, 2E4MZ available from Shikoku ChemicalsCorporation). Subsequently, the same procedure as in Example 1-1 isperformed, thereby forming a sheet-shaped structure with hollows(extension: less than 5%).

(Comparative Example 1-2)

First, the same components as used in Comparative Example 1-1 areuniformly mixed. Subsequently, the same procedure as in Example 2-1 isperformed, thereby forming a sheet-shaped structure with a hollow(extension: less than 5%).

(Comparative Example 1-3)

First, the same components as used in Comparative Example 1-1 areuniformly mixed. Subsequently, the same procedure as in Example 3-1 isperformed, thereby forming a sheet-shaped structure with a hollow(extension: less than 5%).

(Comparative Example 2-1)

First, a 50 micrometers-thick polyethylene naphthalate (PEN) film(available from Teijin DuPont Films) is molded at 200 degrees Celsiusfor one hour using the same mold with the raised pattern as used inExample 1-1, thereby forming a sheet with a recessed pattern. Meanwhile,the same resin composition mixture as obtained and used in Example 1-1is laid as a 10 micrometer-thick adhesive layer on the flat PEN film.Next, the above-mentioned sheet with the recessed pattern is bonded tothis adhesive layer and thermally cured, thereby forming a sheet-shapedstructure with hollows (extension: less than 10%).

(Comparative Example 2-2)

First, the same 50 micrometers-thick PEN film as used in ComparativeExample 2-1 is molded at 200 degrees Celsius for one hour using the sameembossed mold as used in Example 2-1, thereby forming a sheet with araised embossed pattern. Meanwhile, the same the same resin compositionmixture as obtained and used in Example 1-1 is laid as a 20micrometer-thick adhesive layer on the flat PEN film. Next, theabove-mentioned embossed sheet is bonded to the adhesive layer andthermally cured, thereby forming a sheet-shaped structure with a hollow(extension: less than 10%). However, the embossed parts on the embossedsheet have heights varying in the range of 10 to 30 micrometers and arealso curled.

(Comparative Example 2-3)

First, the same resin composition mixture as obtained and used inExample 1-1 is laid as a 10 micrometer-thick adhesive layer on thesurface of the same 50 micrometers-thick PEN film as used in ComparativeExample 2-1. Next, glass beads spacers with a diameter of 20 micrometersare sprayed and arranged at appropriate intervals on the adhesive layer.Another PEN film is then laid on the first PEN film so that the beadsspacers are sandwiched between the two films. The laminated films arethen heated at 170 degrees Celsius for one hour, thereby forming asheet-shaped structure with a hollow.

(Evaluation: Confirmation of Stretchability)

First, the sheet-shaped structures formed in the above-describedexamples and comparative examples are extended by either 10% or 30%while both ends of each structure are held. Next, the extension stressis released to confirm the state of the restored structure. The resultsare evaluated using the following criteria.

After being extended, each structure is evaluated as follows: ifrestored without being partially or completely broken, the structure isevaluated as OK; if not restored although not partially or completelybroken, the structure is evaluated as NG; and if partially or completelybroken, the structure is evaluated as Broken NG. The results are shownin Table 1.

TABLE 1 10% 30% extension/restoration extension/restoration Example 1-1OK OK Example 1-2 OK OK Example 1-3 OK OK Example 1-4 OK OK Example 2-1OK OK Example 2-2 OK OK Example 2-3 OK OK Example 2-4 OK OK Example 3-1OK OK Example 3-2 OK OK Example 3-3 OK OK Example 3-4 OK OK Example 3-5OK OK Comparative Example 1-1 Broken NG Broken NG Comparative Example1-2 Broken NG Broken NG Comparative Example 1-3 Broken NG Broken NGComparative Example 2-1 NG NG Comparative Example 2-2 NG NG ComparativeExample 2-3 NG NG

As apparent from Table 1, all structures in Examples are evaluated as OKeven after being extended by 30%, whereas those in Comparative Examples1-1 to 1-3 are evaluated as Broken NG. The structures in ComparativeExamples 2-1 to 2-3 partly using the same materials as those in Examplesare not broken, but are evaluated as NG. Thus, only those structuresthat include a plurality of laminated stretchable resin sheets 2 can berestored without being partially or completely broken after beingextended.

Example 4 Production of a Stretchable Display Member Using anElectrophoretic Solution

(Example 4-1)

First, 0.1 g of carbon nanotube SWCNT, (IsoNanotubes-M available fromNanoIntegris) is weighed and added to 500 g of an aqueous solution ofsodium dodecyl sulfate with a concentration of 5 wt %. The resultingmixture is dispersed by ultrasonic waves for 24 hours, thereby preparingan aqueous solution dispersed with carbon nanotube (CNT) with aconcentration of 0.02 wt %.

Next, this aqueous solution dispersed with CNT is coated on both sidesof the sheet-shaped stretchable structure with hollows 7 formed inExample 1-1, dried at 120 degrees Celsius for 30 minutes to remove thesolvent, thereby forming a conductive layer on each of the both sides ofthe structure.

Next, the following materials are put in a high-boiling-point solvent(Isoper-M available from Maruzen Petrochemical. Co, Ltd.): positivelycharged black particles (carbon black available from Mitsubishi ChemicalCorporation); negatively charged white particles (titanium oxideavailable from Tayca Corporation); dispersant (Solsperse 17000 availablefrom Lubrizol Corporation); and a charge control agent (SPAN-85, areagent). The resulting mixture is dispersed ultrasonically to preparean electrophoretic solution. This solution is injected using a syringeinto hollows 7 of the structure having the above-described conductivelayers thereon.

Finally, the inlet is sealed using an UV adhesive, thereby forming adisplay element member.

(Example 4-2)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 1-2 is used as asheet-shaped stretchable structure with hollows 7.

(Example 4-3)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 1-3 is used as asheet-shaped stretchable structure with hollows 7.

(Example 4-4)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 1-4 is used as asheet-shaped stretchable structure with hollows 7.

(Example 4-5)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 2-1 is used as asheet-shaped stretchable structure with hollow 7.

(Example 4-6)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 2-2 is used as asheet-shaped stretchable structure with hollow 7.

(Example 4-7)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 2-3 is used as asheet-shaped stretchable structure with hollow 7.

(Example 4-8)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 2-4 is used as asheet-shaped stretchable structure with hollow 7.

(Example 4-9)

A display element member is formed in the same manner as in Example 4-1except that the structure formed in Example 3-5 is used as asheet-shaped stretchable structure with hollow 7.

Furthermore, for comparison, different display element members areprepared by sealing the electrophoretic solution prepared by the samemethod as in Example 4-1 into the sheet-shaped structures formed inComparative Examples 1-1 to 1-3 and 2-1 to 2-3. The obtained displayelement members, however, have been confirmed to have been broken orhave not been restored as shown in Table 1.

(Evaluation: Confirmation of Display Properties)

A voltage is applied to the conductive layers of each of the displayelement members formed in Examples 4-1 to 4-9 and it has been confirmedthat each of the display element members displays in white on thenegative side and in black on the positive side. It has also beenconfirmed that these display element members provide similar displaycapabilities even when extended by 10% or 30% and also when restoredafter being extended.

The conductive layer can be partially patterned by laser etching so asto provide displays shown in FIGS. 13A and 13B. FIG. 13A shows a whitedisplay by applying a potential of −15V to the front surface and apotential of +15V to the rear surface, respectively. In contrast, when apotential of +15V is applied to the front surface and a potential of−15V is applied to the rear surface by reversing the polarity of theapplied voltage, the conductive surface is displayed in black, allowinglaser-patterned letters to appear as shown in FIG. 13B.

Example 5 Production of a Stretchable Display Member Using a CholestericLiquid Crystal

(Example 5-1)

The aqueous solution dispersed with CNT formed in the same manner as inExample 4-1 is coated on both sides of the sheet-shaped structure withhollow 7 formed in Example 3-1. This structure is dried at 120 degreesCelsius for 30 minutes to remove the solvent, thereby forming aconductive layer on each of the both sides of the structure.

Next, a cholesteric liquid crystal (RDP-A3435CH1 available from DICcorporation) is injected using a syringe into hollow 7 of the structureincluding the conductive layer. The inlet is sealed using an UVadhesive, thereby forming a display element member.

(Example 5-2)

A display element member is formed in the same manner as in Example 5-1except that the structure formed in Example 3-2 is used as thesheet-shaped stretchable structure with hollow 7.

(Example 5-3)

A display element member is formed in the same manner as in Example 5-1except that the structure formed in Example 3-3 is used as thesheet-shaped stretchable structure with hollow 7.

(Example 5-4)

A display element member is formed in the same manner as in Example 5-1except that the structure formed in Example 3-4 is used as thesheet-shaped stretchable structure with hollow 7.

(Evaluation: Confirmation of Display Properties)

A voltage is applied to the conductive layers of the display membersformed in Examples 5-1 to 5-4 and it has been confirmed that the displaymembers display in white on the positive side and in black on thenegative side. It has also been confirmed that these display membersprovide similar display capabilities even when extended by 10% or 30%and also when restored after being extended.

Example 6 Production of a Stretchable Electronic Circuit MemberIncluding an Electronic Component

A stretchable electronic circuit member of Example 6, which includes anelectronic component, is formed according to the procedure shown in FIG.6.

(Example 6-1)

One flat stretchable resin sheet 2F with a thickness of 50 micrometersis formed in the same manner as in Example 1-1. In addition, stretchableresin sheet 2E with a recessed pattern is prepared. The recessed patternis molded in a mold with a raised pattern in such a manner that therecessed parts have a height of 200 micrometers.

Meanwhile, a stretchable conductive paste is prepared by fillingurethane resin (HUX-561 available from Adeka Corporation) with 90 wt %of silver particles with a diameter of 2.1 micrometers. This conductivepaste is formed into wires 9A and lands 9B on the surface of sheet 2Eshown in FIG. 6. Next, LED 10 is installed in hollow 7 and is connectedto lands 9B using an electrically conductive adhesive.

Next, sheets 2F and 2B are bonded together and heated at 170 degreesCelsius for one hour, thereby forming an electronic circuit member inWhich LED 10 is sealed. Finally, after the sheets are laser-drilled,vias 12 and wires 9A are printed using the above-described stretchableconductive paste and then connected to an external power supply.

(Example 6-2)

An electronic circuit member is formed in the same manner as in Example6-1 except that the sheet-shaped stretchable structure with hollow 7 isformed by using the materials and method employed in Example 1-2.

(Example 6-3)

An electronic circuit member is formed in the same manner as in Example6-1 except that the sheet-shaped stretchable structure with hollow 7 isformed by using the materials and method employed in Example 1-3.

(Example 6-4)

An electronic circuit member is formed in the same manner as in Example6-1 except that the sheet-shaped stretchable structure with hollow 7 isformed by using the materials and method employed in Example 1-4.

(Evaluation: Confirmation of the Behavior of the Electronic CircuitMember)

A current is applied to the circuits of the electronic circuit membersformed in Examples 6-1 to 6-4 and it has been confirmed that LED 10operates properly. It has also been confirmed that the electroniccircuit members operate properly even when extended by 10% or 30% andalso when restored after being extended.

The aforementioned results indicate that the stretchable structure ofthe present exemplary embodiment is useful as various electronicselements.

Second Exemplary Embodiment

Prior to describing a second exemplary embodiment of the presentdisclosure, problems associated with the conventional techniques willnow be briefly described. Thermosetting resins are widely used, forexample, as electronic and optical materials because of their excellencein heat resistance, chemical resistance, moldability, insulationreliability, etc. Among thermosetting resins, epoxy resins are used forvarious applications. Epoxy resins are excellent in the above-describedproperties, but their hardness and inflexibility are also well known.Because of these undesirable properties, epoxy resins can be deformed orbroken due to external stress or heat stress.

Examples of more flexible materials include the following: siliconeresins, urethane resins, thermoplastic resins such as polyethylene, andvarious rubber materials. Regarding the flexibility of resin materials,not only a low elastic modulus and a high tensile elongation, but alsoexcellent restoration properties after extension are required to be usedas various applications.

Meanwhile, recent resin materials need to have stress relaxationproperties as well as flexibility. Having a large residual stress whendeformed under stress means having a large restoring force.Consequently, a large residual stress causes exfoliation betweencomponents or their breakage. To avoid this, resin materials need tohave the property of reducing an applied stress and hence the residualstress, that is, to have excellent stress relaxation properties.

Urethane resins and silicone resins described in the aforementionedUnexamined Japanese Patent Publication No. 2012-63437 and No.2012-27488, however, are known to be poor in stress relaxationproperties although they are excellent in tensile elongation andrestoration properties.

In the electronics field, every component should have such properties asheat resistance of its material and adhesion with other components.Thermoplastic resins such as urethane resins are known to reversiblymelt when heated, whereas silicone resins are known to have low surfacetension. These properties of the conventional resins, such as meltingwith heat and low surface tension may make it difficult to ensureadhesion with other components.

As a result, display devices including these resins are easilyexfoliated or broken due to residual stress because of elasticdeformability or low surface tension when caused to fit a curved surfaceor to accommodate large deformation.

These problems hold true for other rubber materials, and highlyrestorable materials generally have low stress relaxation properties. Onthe other hand, polyethylene and other thermoplastic materials are usedin various fields by taking advantage of their flexibility and hightensile elongation. However, the tensile elongation is in the range onlyfrom several to several dozen percent, and at stresses exceeding theyield point, these thermoplastic materials are plastically deformed andextended. As a result, these materials cannot be restored afterextension (due to many residual strains) although having excellentstress relaxation properties.

Resin materials have been extensively studied concerning their lowelasticity, softness with high extensibility, and restorationproperties. However, as compared with these properties, it has rarelybeen reported to successfully improve stress relaxation properties. Thereason for this is considered that stress relaxation is caused byplastic deformation due to creep phenomena and that it is impossible torestore plastically deformed resin materials.

Hereinafter, the second exemplary embodiment of the present disclosurewill now be described, but the present disclosure is not limited to thisembodiment. The present exemplary embodiment deals with materials havingthe following properties: high stress relaxation properties whenstretched; excellent restoration properties after extension; highability to prevent exfoliation and breakage of components due toresidual stress; and high adhesion.

The stretchable resin sheet, which is the cured material of the resincomposition used in the electronics element of the present exemplaryembodiment, has elastic deformability and few residual strains and alsohas stress relaxation properties. More specifically, when apredetermined amount of deformation is of the stretchable resin sheet,the stress causing the deformation decreases with time. When the stressreduces to zero, the stretchable resin sheet is restored substantiallyto its original shape.

Thus, materials having flexibility and stress relaxation properties canbe achieved by balancing high stress relaxation properties whenstretched and excellent restoration properties after extension.

In the present exemplary embodiment, the term “elastic deformability andfew residual strains” specifically means to be plasticallynon-deformable and the residual strain rate is preferably not more than3%. The term “to have stress relaxation properties” specifically meansto have the ability to reduce an applied force (for example, tensileforce) so as to reduce the residual stress.

In the present exemplary embodiment, for convenience, the residualstrain and stress relaxation properties of the resin composition forstretchable resin sheet are defined as stress relaxation rate R andresidual strain rate alpha, respectively, which are measured by anafter-mentioned extension-restoration. test.

In the stretchable resin sheet as the cured material of the resincomposition of the present exemplary embodiment, it is preferable thatthe stress relaxation rate R be in a range from 20% to 95%, inclusive,and the residual strain rate alpha be in a range from 0% to 3%,inclusive, and it is more preferable that the stress relaxation rate Rbe in a range from 30% to 60%, inclusive, and the residual strain ratealpha be in a range from 0% to 1.5%, inclusive. When these conditionsare satisfied, the resin composition for stretchable resin sheet of thepresent exemplary embodiment can have both high stress relaxationproperties when stretched and excellent restoration properties afterextension.

A resin composition of which cured material has the stress relaxationrate and the residual strain rate within the above-mentioned ranges canbe formed into a cured material having both high stress relaxationproperties when stretched and excellent restoration properties afterextension, thereby having high flexibility and excellent stressrelaxation properties.

In the present exemplary embodiment, the “cured material” of the resincomposition for stretchable resin sheet means a resin that is obtainedby subjecting a curable resin composition to a curing reaction withsufficient energy such as heat or light. The cured material of thepresent exemplary embodiment does not become plastic again by heating.Thus, the cured material is heat resistant, insoluble, and infusible.

(Extension-Restoration Test)

In the extension-restoration test conducted in the present exemplaryembodiment, pieces of the stretchable resin sheet as the cured materialof the resin composition for stretchable resin sheet are subjected to anextension process and a restoration process under the conditions shownbelow, using a tensile-compression tester according to ISO 3384. Then,the stress relaxation rate R and the residual strain rate alpha arecalculated by the calculation methods shown below. Each of thestretchable resin sheet pieces to be tested has a thickness of 50micrometers and a shape of dumbbell No. 6 (the width of the portion tobe measured: 4 mm, and the length of the parallel portion: 25 mm). Thetensile-compression tester can be, for example, AutoGraph (type: AGS-X)available from Shimadzu Corporation.

(The Extension Process Conditions)

Deflection is corrected with a force of not more than 0.05N in order toeliminate the deflection developed when each test piece is attached to acramp under the following conditions:

-   -   speed of testing: extended at 25 mm/min from a non-stretched        state to 25%    -   temperature: 23 degrees Celsius    -   extension/holding conditions: holding for 5 minutes at 25%        extension

(The Restoration Process Conditions)

-   -   speed of testing: 0.1 mm/min until the tensile force reaches        0±0.05 N    -   temperature: 23 degrees Celsius

Stress relaxation rate R calculation method: the tensile force ismeasured at the time when the extension process is completed, anddefined as initial tensile force F_(A0). After the amount of strain isheld for 5 minutes under the above extension/holding conditions, thetensile force is measured and defined as F_(A)(t5).

The stress relaxation rate R is calculated by the formula shown below.

$R = {\frac{F_{A\; 0} - {F_{A}\left( {t\; 5} \right)}}{F_{A\; 0}} \times 100}$

Residual strain rate alpha calculation method: the amount of strain ismeasured at the time when the tensile force reaches 0±0.05 N in therestoration process, and the amount of strain is defined as the residualstrain rate alpha.

In the above extension-restoration test, the cured material of the resincomposition of the present exemplary embodiment (the resin sheetobtained by curing the resin composition of Example 7-2 described later)shows an extension (strain) restoration behavior with respect to thetensile force as shown by a curved or nearly straight line in the graphshown in FIG. 14. In FIG. 14, the vertical axis represents a tensileforce (test force) expressed in N/mm², and the horizontal axisrepresents the amount of extension (strain) expressed in %. The term“the amount of extension” means a substantial amount of strain of thestretchable resin sheet.

FIG. 14 also shows, for comparison, the results of theextension-restoration test for evaluating the behavior of twoconventional resin films. One is a silicone film made of elasticallydeformable resin (the resin sheet obtained by curing the resincomposition of Comparative Example 7-4 described later), and the otheris a polyethylene film made of plastically deformable resin (the resinsheet obtained by curing the resin composition of Comparative Example7-5 described later). For either film, the upper curved or nearlystraight line represents extension in the extension process, and thelower curved or nearly straight line represents restoration (return fromthe extension) in the restoration process.

As shown in FIG. 14, the stretchable resin sheet of the presentexemplary embodiment is extended up to 25% according to the tensileforce in the extension process, is retained for 5 minutes. However, thestretchable resin sheet of the present exemplary embodiment reduces thestress while retained in the extension state, and is restored until thetensile force reaches 0±0.05 N in the restoration process.

The stretchable resin sheet of the present exemplary embodiment isrestored until the residual strain is reduced to about 1% after theextension-restoration test. Thus, the stretchable resin sheet has verylow residual strain rate.

On the other hand, in the polyethylene film, the residual strain is onlyreduced to about 8.4% after the extension-restoration test. Thus, thepolyethylene film has high residual strain rate. When retained for 5minutes after the extension process, the stress of the polyethylene filmis reduced by about 30%, while the stress of the extended silicone filmis hardly reduced.

In contrast, the stress of the resin composition of the presentexemplary embodiment is reduced by about 30%.

The behavior of the stretchable resin sheet of the present exemplaryembodiment shown in FIG. 14 also indicates that the cured material ofthe resin composition of the present exemplary embodiment hasflexibility, excellent restoration properties after extension, and alsoexcellent stress relaxation properties. These are unique andadvantageous properties not observed in the conventional elastically andplastically deformable resins. Therefore, the resin composition forstretchable resin sheet of the present exemplary embodiment can exerciseits properties in flexible display devices and other similar devices.

As another preferred exemplary embodiment, the resin compositionpreferably contains an uncross-linked curing resin component and has theproperties of being remelted or softened when heated and a thermosettingproperty or a photocurable property. In short, it is preferable that theresin composition be a semi-cured film-like resin composition. Theseconfigurations allow preparing a resin composition with excellentadhesion and moldability.

The resin composition containing uncross-linked curing resin components,that is, unreacted functional groups in reactive resin components allowsthe unreacted functional groups to bind covalently to, for example,hydroxyl groups existing on a surface of a laminated plate, a metal, orglass. This improves the adhesion between the resin materials and them.More specifically, it is preferable that some of the functional groupsof the reactive resin components be cross-linked and the remaining largenumber of functional groups be uncross-linked. This chemical structureallows the resin composition for stretchable resin sheet of the presentexemplary embodiment to be formed into a semi-cured base member or filmthat can be easily handled when bonded or laminated

Because of having the property of being remelted or softened whenheated, the resin composition for stretchable resin sheet of the presentexemplary embodiment can be molded into various complicated shapes.Resin compositions having a melt viscosity of 100 to 100000 cps at 80 to150 degrees Celsius desirably have excellent moldability. Resincompositions having a melt viscosity of 500 to 50000 cps at 80 to 130degrees Celsius desirably have excellent compactability (repletion)because they are unlikely to have voids during molding.

It is also preferable that the resin composition for stretchable resinsheet contain a curing agent and epoxy resin as thermosetting resin.This allows the stretchable resin sheet to be excellent not only inelectrical insulation, heat resistance, chemical resistance, andtoughness, but also in workability because of its compatibility withvarious resins.

The resin composition for stretchable resin sheet can include, forexample, at least the following: (A) polyrotaxane, (B) thermosettingresin, and (C) a curing agent. If necessary, (D) a cross-linking agentmay be added. Each of these components will now be described in detail.

Component A: Polyrotaxane

A polyrotaxane has a chemical structure in which a linear axle moleculepenetrates circular molecules and the terminals of the linear axlemolecule are blocked to prevent dissociation of the circular molecules.More specific examples include the polyrotaxane disclosed in JapanesePatent No. 4482633.

Examples of the polyrotaxane that can be used in the present exemplaryembodiment include the following compounds: those in which an axlemolecule having terminal functional groups is enclathrated in a skeweredstate in circular molecules, and the terminal functional groups arechemically modified with a blocking group bulky enough to preventdissociation of the circular molecules. Any polyrotaxanes with such astructure can be used regardless of the structure and type of themolecules composing them or the enclathration rate and the synthesismethod of the circular molecules.

The axle molecule that can be contained in a polyrotaxane is notparticularly limited as long as it has a molecular weight of not lessthan 10000 and each of the terminals can be chemically modified with ablocking group. Examples of such an axle molecule include the following:polyvinyl alcohol, polyvinylpyrrolidone, poly(meth)acrylic acidcellulosic resin, polyacrylamide, polyethylene oxide, polyethyleneglycol, polypropylene glycol, polyvinyl acetal-based resin, polyvinylmethyl ether, polyamine, polyethylenimine, casein, gelatin, starch,polyolefin, polyester, polyvinyl chloride, polystyrene,acrylonitrile-styrene copolymer and other copolymers, acrylic-basedresin, polycarbonate, polyurethane, polyvinyl butyral, polyisobutylene,polytetrahydrofuran, polyamide, polyimide, polythene, polysiloxane,polyurea, polysulfide, polyphosphazene, polyketone, polyphenylene,polyhaloolefin, and their derivatives. Among them, polyethylene glycolis preferable.

Any circular molecule can be contained in the polyrotaxane as long as itallows a polymer molecule to pass through it and has at least onereaction group so as to react with a cross-linking agent. Examples ofsuch a circular molecule include the following: cyclodextrins, crownethers, cryptands, macrocyclic amines, calixarenes, and cyclophanses.Among them, cyclodextrins and substituted cyclodextrins are preferable.More preferable examples are those in which a reaction group (functionalgroup) is introduced into the substituted structure.

Preferable examples of the functional group to he introduced into thecircular molecules of the polyrotaxane include the following: hydroxylgroup, carboxyl group, acrylic group, methacrylic group, epoxy group,and vinyl group.

The functional group introduced into the circular molecules cancross-link either the circular molecules, or the polyrotaxane and theresin via a cross-linking agent. The resin cross-linked with thepolyrotaxane described above has flexibility.

The configuration (end-capping group) to block the terminals of thepolyrotaxane used in the present exemplary embodiment is notparticularly limited as long as it is bulky enough to preventdissociation of the circular molecules. Preferable examples of such agroup include the following: cyclodextrin group, adamantane group,dinitrophenyl group, and trityl group.

The circular molecule to be used is not particularly limited as long asit can enclathrate chain polymer molecules in its ring. A preferableexample of the circular molecule is cyclodextrin. It is preferable thateach of the circular molecules has a functional group. It is alsopreferable that the functional group be one of hydroxyl group, acrylicgroup, and methacrylic group.

The polyrotaxane used in the present exemplary embodiment can besynthesized by well-known methods such as those shown in InternationalPublication No. 2001/83566, Unexamined Japanese Patent Publication No.2005-154675, and Japanese Patent No. 4482633. Alternatively, anycommercially available polyrotaxanes can be used, such as SeRM superpolymer SH3400P and SH2400P available from Advanced Softmaterials Inc.

Component B: Thermosetting Resin

As the thermosetting resin, epoxy resin, phenol resin, polyimide resin,urea resin, melamine resin, unsaturated polyester, and urethane resincan be used without any limitation. Among them, epoxy resin ispreferable.

Examples of the epoxy resin include the following: bisphenol A epoxyresin, bisphenol F epoxy resin, bisphenol S epoxy resin, aralkyl epoxyresin, phenol novolac epoxy resin, alkyl phenol novolac epoxy resin,biphenol epoxy resin, naphthalene epoxy resin, dicyclopentadiene epoxyresin, an epoxy compound of a condensation product of a phenol and anaromatic aldehyde with a phenolic hydroxyl group, triglycidylisocyanurate, and alicyclic epoxy resin. They may be used alone or incombination of two or more thereof depending on the situation.

The epoxy resin more preferably has two or more epoxy groups and threeor more methyl groups per molecule and has a molecular weight of notless than 500. The epoxy resin can be any commercially available onesuch as follows: JER1003 (available from Mitsubishi ChemicalCorporation, which is bifunctional and has 7 to 8 methyl groups and amolecular weight of 1300); EXA-4816 (available from DIC corporation,which is bifunctional and has a molecular weight of 824 and many methylgroups); and YP-50 (available from Nippon Steel & Sumikin Chemical Co.,Ltd., which is bifunctional and has molecular weight of 60,000 to 80,000and many methyl groups).

It is preferable that the curing resin which contain Components A and Bbe at least partially uncross-linked. In other words, it is preferablethat the functional group of Component A be uncross-linked, and at leastone and preferably both of the epoxy groups of Component B beuncross-linked. It is more preferable that some of the functional groupsand/or the epoxy groups contained in the reactive resin (curing resin)composed of Components A and B be cross-linked, and the remaining largenumber of groups be uncross-linked. This allows the resin composition tobe formed into a semi-cured base member or film that can be easilyhandled when bonded or laminated.

The resin composition in which the curing resin is in an uncross-linkedstate (semi-cured state) can be prepared by adjusting the heating anddrying conditions as described later.

Component C: Curing Agent

The curing agent is not particularly limited as long as it can functionfor the thermosetting resin of Component B. Preferable examples of thecuring agent for the epoxy resin include the following: phenol resin,amine-based compounds, acid anhydrides, imidazole-based compounds,sulfide resins, and dicyandiamides. light (ultraviolet) curing agentsand thermal cationic curing agents can be used. They may be used aloneor in combination of two or more thereof depending on the situation.

Component D: A Cross-Linking Agent

It is possible to add a cross-linking agent to the resin composition forstretchable resin sheet of the present exemplary embodiment containingthe polyrotaxane. The cross-linking agent is not particularly limited aslong as it can form a cross-linking structure between at least part (atleast one reaction group in the circular molecules of the polyrotaxane)of the circular molecules of the polyrotaxane and Component C of thecuring agent.

Examples of the cross-linking agent include the following: isocyanate,cyanuric chloride, trimesoyl chloride, terephthaloyl chloride,epichlorohydrin, dibromobenzene, glutaraldehyde, phenylene diisocyanate,tolylene diisocyanate, divinyl sulfone, 1,1-carbonyldiimidazole, andalkoxysilane. One example of the isocyanates is DN-950 (available fromDIC corporation).

In the present exemplary embodiment, the number of the functional groupscontained in the cross-linking agent is not limited. It is preferable,however, that the cross-linking agent has two or more functional groupsper molecular in order to cross-link either the circular molecules ofthe polyrotaxane, or the circular molecules and an after-mentionedresin. When the cross-linking agent has two or more functional groups,the groups may be the same or different from each other.

It is more preferable that the cross-linking agent be compatible withthe polyrotaxane. In the case of using, as Component A, a polyrotaxanecontaining circular molecules having hydroxyl group, it is preferable touse an isocyanate or its derivative as the cross-linking agent. Theisocyanate resin can be any kind, such as blocked isocyanate resinobtained by blocking the isocyanate groups.

On the other hand, in the case of using, as Component A, a polyrotaxanecontaining circular molecules having either acrylic group or methacrylicgroup, acrylic resin can be added as reactive resin. The acrylic resincan also be of any type.

The contents of the components in the resin composition of the presentexemplary embodiment are not limited as long as the effects of thepresent disclosure can be provided. More specifically, Component A ispreferably 10 to 80 parts by weight, and more preferably 30 to 50 partsby weight; Component B is preferably 10 to 89.9 parts by weight, andmore preferably 30 to 50 parts by weight; Component C is preferably 0.1to 30 parts by weight, and more preferably 0.1 to 20 parts by weight,with respect to 100 parts by weight of the total amount of Components Ato C. In the case of using the isocyanate resin as the cross-linkingagent of Component D, the content of the isocyanate resin to be added tothe polyrotaxane of Component A is 0 to 50 parts by weight, andpreferably 10 to 40 parts by weight.

As long as being able to ensure the effects of the present disclosure,the resin composition for stretchable resin sheet of the presentexemplary embodiment can contain other additives such as a curingcatalyst (curing accelerator), a flame retardant, a flame retardantauxiliary agent, a leveling agent, and a colorant according to the need.

The method of preparing the resin composition for stretchable resinsheet of the present exemplary embodiment containing the polyrotaxane ofComponent A is not particularly limited. For example, a polyrotaxane, acuring agent, a cross-linking agent, thermosetting resin, and a solventcan be uniformly mixed to prepare the resin composition. The solvent canbe of any type such as, toluene, xylene, methyl ethyl ketone, andacetone. These solvents may be used alone or in combination of two ormore thereof. It is also possible to add an organic solvent to modifythe viscosity, and various additives according to the need.

The obtained resin composition for stretchable resin sheet containingthe polyrotaxane of Component A is heat-dried for curing while thesolvent is being evaporated off, thereby forming a stretchable resinsheet.

The resin composition for stretchable resin sheet containing thepolyrotaxane of Component A can be heat-dried using any of theconventional and improved methods, devices, and conditions. Thetemperature and time of the heating can be properly determined accordingto the used cross-linking agent and the solvent. For example, the resincomposition for stretchable resin sheet can be obtained by heat-dryingfor 60 to 120 minutes at 50 to 200 degrees Celsius for curing the resincomposition.

Other examples of the resin composition for stretchable resin sheet ofthe present exemplary embodiment include a resin composition containingComponents E and F described below. Component E is an epoxy resin havingan alkylene oxide-modified group having 2 to 3 carbon atoms. In thisepoxy resin, 4 mol or more of the modified groups, and not less than 2mol of epoxy groups are contained per mol of epoxy molecules. The epoxyequivalent weight is not less than 450 eq/mol. Meanwhile, Component F isa curing agent. Examples of Components E and F will now be described asfollows.

Examples of the epoxy resin of Component E include the following: apropylene oxide adduct of bisphenol A epoxy resin (EP4003S availablefrom ADEKA Corporation), and an ethylene oxide adduct of hydroxyphenylfluorene epoxy resin (EG-280 available from Osaka Gas Chemicals Co.,Ltd.).

As long as being able to ensure the effects of the present disclosure,the resin composition for stretchable resin sheet of the presentexemplary embodiment containing the epoxy resin of Component E mayfurther contain an epoxy resin other than Component E. Examples of theepoxy resin other than Component E include the following: bisphenol Aepoxy, bisphenol F epoxy, bisphenol S epoxy, aralkyl epoxy, aliphaticepoxy, and alicyclic epoxy. The content of Component E in the entireepoxy resin component is approx. 60 to 99 wt %, and preferably approx.80 to 95 wt %.

The curing agent of Component F can be any well-known curing agent forepoxy resin. To be more specific, phenol resins, acid anhydrides, andsulfonium salt are preferable because of their curability. If necessary,it is also possible to combine a curing accelerator such asimidazole-based compounds, together with two or more selected from theabove-mentioned curing agents.

The phenol resin curing agents can be of any of monomers, oligomers, andpolymers as long as it has two or more phenolic hydroxyl groups permolecule. The molecular weight and molecular structure of the phenolresin curing agent are not particularly limited. One example of thephenol resin curing agent is a resin obtained by condensing orco-condensing a phenol, a naphthol such as an α-naphthol, β-naphthol,and a dihydroxynaphthalene, and a compound having an aldehyde group suchas formaldehyde under an acidic catalyst. Another example is a phenolaralkyl resin synthesized from a phenol and/or a naphthol and eitherdimethoxyparaxylene or bis(methoxymethyl)biphenyl. Examples of thephenol include the following: phenols such as phenol novolac resin andcresol novolac resin, cresol, resorcin, catechol, bisphenol A, bisphenolF, phenylphenol, and aminophenol. They may be used alone or incombination of two or more thereof.

Examples of the acid anhydride curing agent include the following:maleic anhydride, succinic anhydride, itaconic anhydride, citraconicanhydride, phthalic anhydride, 1,2,3,6-tetrahydrophthalic anhydride,3,4,5,6-tetrahydrophthalic anhydride, hexahydrophthalic anhydride,4-methylhexahydrophthalic anhydride, 3-methyl-1,2,3,6-tetrahydrophthalicanhydride, 4-methyl-1,2,3,6-tetrahydrophthalic anhydride, andmethyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride.

Examples of the sulfonium salt include the following: alkylsulfoniumsalt, benzylsulfonium salt, dibenzylsulfonium salt, and substitutedbenzylsulfonium salt. Examples of the alkyl sulfonium salt include thefollowing: 4-acetophenyldimethyl sulfonium hexafluoroantimonate,4-acetoxyphenyldimethyl sulfonium hexafluoroarsenate,dimethyl-4-(benzyloxycarbonyloxy)phenyl sulfonium hexafluoroantimonate,dimethyl-4-(benzoyloxy)phenyl sulfonium hexafluoroantimonate,dimethyl-4-(benzoyloxy)phenyl sulfonium hexafluoroarsenate, anddimethyl-3-chloro-4-acetoxyphenyl sulfonium hexafluoroantimonate.Examples of the benzylsulfonium salt include the following:benzyl-4-hydroxyphenylmethyl sulfonium hexafluoroantimonate,benzyl-4-hydroxyphenylmethyl sulfonium hexafluorophosphate,4-acetoxyphenylbenzylmethyl sulfonium hexafluoroantimonate,benzyl-4-methoxyphenylmethyl sulfonium hexafluoroantimonate,benzyl-2-methyl-4-hydroxyphenylmethyl sulfonium hexafluoroantimonate,benzyl-3-chloro-4-hydroxyphenylmethyl sulfonium hexafluoroarsenate, and4-methoxybenzyl-4-hydroxyphenylmethyl sulfonium hexafluorophosphate.Examples of the dibenzylsulfonium salt include the following:dibenzyl-4-hydroxyphenyl sulfonium hexafluoroantimonate,dibenzyl-4-hydroxyphenyl sulfonium hexafluorophosphate,4-acetoxyphenyldibenzyl sulfonium hexafluoroantimonate,dibenzyl-4-methoxyphenyl sulfonium hexafluoroantimonate,dibenzyl-3-chloro-4-hydroxyphenyl sulfonium hexafluoroarsenate,dibenzyl-3-methyl-4-hydroxy-5-tert-butylphenyl sulfoniumhexafluoroantimonate, and benzyl-4-methoxybenzyl-4-hydroxyphenylsulfonium hexafluorophosphate. Examples of the substitutedbenzylsulfonium salt include the following:p-chlorobenzyl-4-hydroxyphenylmethyl sulfonium hexafluoroantimonate,p-nitrobenzyl-4-hydroxyphenylmethyl sulfonium hexafluoroantimonate,p-chlorobenzyl-4-hydroxyphenylmethyl sulfonium hexafluorophosphate,p-nitrobenzyl-3-methyl-4-hydroxyphenylmethyl sulfoniumhexafluoroantimonate, 3,5-dichlorobenzyl-4-hydroxyphenylmethyl sulfoniumhexafluoroantimonate, and o-chlorobenzyl-3-chloro-4-hydroxyphenylmethylsulfonium hexafluoroantimonate.

One example of the polyfunctional phenolic curing agent is GPH-103(available from Nippon Kayaku Co., Ltd., which is biphenyl aralkylphenol). One example of the acid anhydride-based curing agent is YH-306(available from Mitsubishi Chemical Corporation). One example of theimidazole-based curing accelerator is 2E4MZ (available from ShikokuChemicals Corporation, which is 2-ethyl-4-methylimidazole).

The contents of the components in the resin composition for stretchableresin sheet containing the epoxy resin of Component E are not limited aslong as the effects of the present disclosure can be provided. Morespecifically, Component E is preferably 50 to 99 parts by weight, andmore preferably 60 to 80 parts by weight; and Component F is preferably1 to 50 parts by weight, and more preferably 1 to 40 parts by weight,with respect to 100 parts by weight of the total amount of the resincomposition for stretchable resin sheet.

As long as being able to ensure the effects of the present disclosure,the resin composition for stretchable resin sheet containing Component Ecan contain other additives such as a curing catalyst (curingaccelerator), a flame retardant, a flame retardant auxiliary agent, aleveling agent, and a colorant according to the need.

The method of preparing the resin composition for stretchable resinsheet of the present exemplary embodiment containing Component E is notparticularly limited. For example, epoxy resin, a curing agent, and asolvent can be uniformly mixed. The solvent can be of any type such as,toluene, xylene, methyl ethyl ketone, acetone, DMF, NPM, or ethylacetate. These solvents may be used alone or in combination of two ormore thereof. It is also possible to add an organic solvent to modifythe viscosity, or various additives according to the need.

The obtained resin composition for stretchable resin sheet containingComponent E is heat-dried for curing while the solvent is beingevaporated off, thereby forming a stretchable resin sheet.

The resin composition for stretchable resin sheet containing Component Ecan be heat-dried using any of the conventional and improved methods,devices, and conditions. The temperature and time of the heating can beproperly determined according to the used cross-linking agent and thesolvent. For example, the resin composition for stretchable resin sheetcan be obtained by heat-drying for 60 to 180 minutes at 130 to 200degrees Celsius for curing the resin composition.

In the drying conditions of the resin composition for stretchable resinsheets prepared in different manners as above, the volatilization rateof the solvent is much faster than the rate of the curing reaction ofthe resin, and the heat-drying process is suspended when the sheet isdried enough, thereby, a semi-cured film-like resin composition can beformed. The “semi-cured” state means that the resin sheet containsunreacted resin, which may be softened or remelted by heating. Thefilm-like resin composition in the semi-cured state (what is called, aprepreg state) can be thermally molded by using metal molds or the like.In this case, the semi-cured (uncross-linked) resin is considered to becovalently bonded to the hydroxyl groups on the surface of the object tobe bonded, thereby providing high adhesive strength.

In the present exemplary embodiment, the semi-cured film-like resincomposition can be dried using any of the conventional and improvedmethods, devices, and conditions. The temperature and time of the dryingcan be properly determined according to the used cross-linking agent andthe solvent. For example, a semi-cured film-like resin composition forstretchable resin sheet can be obtained by heat-drying for 2 to 15minutes at 80 to 130 degrees Celsius.

The semi-cured film-like resin composition can be used as a support bodyor can be bonded between layers so as to buffer the stress or can bebonded to the surface of a layer so as to protect the surface. Inaddition, the semi-cured film-like resin composition can be cured byheat or light energy so as to provide sufficient heat resistance andadhesion, thereby forming a stretchable structure having a buffer layeror a protective layer with excellent stress relaxation and few residualstrains. It is also possible to bond an object to be supported to thefilm-like resin composition of the present exemplary embodiment and tocure the resin composition with heat or light such as ultraviolet.

It is further preferable that the resin composition for stretchableresin sheet of the present exemplary embodiment contain filler. Usingfiller allows controlling not only the resin strength and the thermalexpansion coefficient, but also water-absorbing properties andelectroconductivity.

The filler can be of various types depending on the application. It ispreferable that the filler contain at least one selected from organicfibers, carbon fibers, glass fibers, and metal fibers. Using such fillerreinforces the resin strength, allowing the stretchable resin sheet tobe pliable and tough. Using such filler also facilitates the control ofthe linear expansion, making the stretchable resin sheet easier to dealwith, more electrically conductive and less expensive. If needed, thesefibers can be surface-treated with a coupling agent or surface-modifiedby graft polymerization by any of conventional and improved methods. Thefiber fabrics can be of any type such as woven and nonwoven.

Examples of the material of the organic fibers include the following:polyethylene, poly(p-phenylenebenzobisoxazole), aramid, polyester,vinylon, polypropylene, nylon, rayon, polylactic acid, polyarylate,polyphenylene sulfide, polyimide, and fluorine resin.

Examples of the glass fiber include yarn-based glass cloth, choppedstrand, and chopped strand sheet formed by machining the chopped strand.

Examples of the metal fibers include fiber fabrics and random mesh ofsteel or silver.

Other examples of the filler can be selected from spherical, crushed,flaky, and discontinuous fiber-like particles. The components of thefiller are not particularly limited and may, for example, contain atleast one substance including an element selected from Si, Cu, Ag, Au,Al, Mg, Pt, and Ti. Using such filler reduces the cost and improves thelinear expansion, electrical conductivity, flame retardance, and opticalproperties such as refractive index. The size and particle diameter ofthe filler are not particularly limited; however, when the particlediameter is in the range from 1 nm to 100 nm, the filler can be used incomparatively small amounts to effectively improve the opticalproperties, electrical conductivity, and linear expansion. Meanwhile,fillers with a particle diameter in the range from 100 nm to 50micrometers are easy to deal with and cost advantageous for manufacture.

Specific examples of the substance including an element selected fromSi, Cu, Ag, Au, Al, Mg, Pt, and Ti include the following particles,flakes, and wires: silica, copper particles, copper-plated particles,silver particles, silver flakes, silver wires, silver-plated particles,gold particles, gold wires, gold-plated particles, aluminum particles,aluminum oxide particles, aluminum hydroxide particles, magnesiumparticles, magnesium hydroxide, magnesium oxide, platinum particles,platinum-plated particles, titanium particles, titanium oxide particles,and titanium oxide-coated particles. They may be used alone or incombination of two or more thereof. These particles, flakes, and wiresmay be used according to any of conventional and improved methods. Morespecifically, filler can be added to a varnish made by dissolving resinin a solvent and dispersed using a dispersing machine such as a beadmill, a jet mill, a planetary stirrer, a homodisper, or an ultrasonicwave disperser.

Still other examples of the filler include carbon nanotubes and/or metalwires. Using such filler is preferable to efficiently provide the resincomposition with electrical conductivity. More specifically, the samelevel of electrical conductivity can be provided by adding smalleramounts of filler than spherical and flaky conductive materials. Thus,such filler is preferable because of its high cost-effectiveness as wellas its easiness to maintain resin properties, allowing the resincomposition to maintain its electrical conductivity when stretched,bent, or deformed in other ways.

These conductive materials can be dispersed in resin by any ofconventional and improved methods. More specifically, a dispersionliquid is prepared by adding filler and a dispersant such as acellulosic or amine- or sulfuric acid-based ionic liquid to a solventsuch as water, methyl isobutyl ketone, methyl ethyl ketone, toluene,acetone, or dimethylformamide. Next, resin is added to the dispersionliquid, and the solvent is removed to disperse the filler into theresin.

The carbon nanotube is not particularly limited in type, but can be, forexample, a single-wall carbon nanotube, a double-wall carbon nanotube,or a multiwall carbon nanotube. These carbon nanotubes can bysynthesized by any of conventional and improved methods. Different typesof carbon nanotubes are used for different purposes; for example, inorder to give priority to electrical conductivity, it is preferable touse a carbon nanotube with high crystallinity, that is, a GM ratio of 10or more when determined by Raman spectroscopy.

Examples of the metal wire include discontinuous metal fibers with highaspect ratio, such as silver nanowires, silver nanorods, and goldnanorods.

The sizes of these carbon nanotubes and metal wires are not particularlylimited; however, when the diameter is not less than 1 nm and not morethan 100 nm and the length is not less than 1 micrometer and not morethan 10 mm, the filler can be well dispersed in the resin so as toimprove electrical conductivity and reinforcement.

The above-enumerated fillers may be used alone or in combination of twoor more thereof.

In the case that the resin composition contains filler, the fillercontent can be properly adjusted according to the use of the stretchableresin sheet; it is preferably not less than 0.05 wt % and not more than80 wt % in general. In this range, the resin properties can bemaintained, and appropriate functions can be provided. A filler contentof less than 0.05 wt % may not allow taking advantage of fillerproperties such as low-thermal expansion, thermal conductivity, andelectrical conductivity. A filler content of more than 80 wt % may notallow taking advantage of resin properties such as stretchability,pliability, and extensibility. The filler content of not less than 0.05wt % and not more than 50 wt % is more preferable because it provideshigh stress relaxation properties and few residual strains.

It is also preferable that the resin composition for stretchable resinsheet of the present exemplary embodiment contain a surface conditioner.

The surface conditioner is added to reduce the surface tension so as toimprove the flatness of the surface of the cured stretchable resinsheet. The improved flatness improves adhesiveness and cohesivenessduring the assembly of the structure including the stretchable resinsheet. The flatness is an important factor also to improve the precisionof the gap space in hollow 7 in the first exemplary embodiment.

The content of the surface conditioner is not particularly limited;however, it is preferably 0.001 wt % to 20 wt %, and more preferably 0.1wt % to 5 wt %. Too low a content tends to reduce the flatness, whereastoo high a content may cause the stretchable resin sheet to be turbid,less heat resistant and less adhesive.

The surface conditioner can be of any type that is added for surfaceconditioning, such as acrylic-, vinyl-, silicone-, and fluorine-basedcompounds.

Examples of the acrylic-based surface conditioner include productsmainly composed of polyalkyl acrylate, polyalkyl methacrylate, or(meth)acrylic copolymer.

Examples of the vinyl-based surface conditioner include products mainlycomposed of polyalkylvinylether or polybutadiene.

Example of the silicone-based surface conditioner include productsmainly composed of polyether-modified polydimethylsiloxane,polyester-modified polydimethylsiloxane, polyether-modifiedpolymethylalkylsiloxane, aralkyl-modified polymethylalkylsiloxane,polyether-modified polydimethylsiloxane, polyether-modified siloxane,polyphenylsiloxane, or polyester-modified hydroxyl group-containingpolydimethylsiloxane.

Examples of the fluorine-based surface conditioner include productsmainly composed of a silicone fluoride or a fluorine-based polymer.

They may be used alone or in combination of two or more thereof.

The stretchable resin sheet of the present exemplary embodiment can beused for various electronic components for various applications. Becauseof its flexibility, stress relaxation properties, and excellentrestoration properties, the stretchable resin sheet has bothstretchability and bendability, and is therefore suitable as a materialfor foldable electronic papers, organic EL displays, solar cells, RFIDs,pressure sensors, etc. Thus, the resin composition of the presentexemplary embodiment can be appropriately used as the resin compositionfor stretchable resin sheet described in the first exemplary embodiment.

Meanwhile, wires can also be fabricated on a support body formed of thestretchable resin sheet of the present exemplary embodiment. The wirescan be fabricated by any known method such as inkjet printing, screenprinting, stencil printing, intaglio printing, relief printing, andplanographic printing.

It is also preferable to use the above-described stretchable resin sheetof the present exemplary embodiment as a film on a support body. Usingthis stretchable resin sheet can achieve a flexible display device whichcan fit any curved surface and accommodate large deformation. The filmmay be formed using any general-purpose coater such as a spin coater, abar coater, or a comma coater.

The support body can be made of any material; for example, rigidmaterial such as glass, metal, and printed wiring board, or flexible,stretchable material such as resin film, flexible substrate, andelastomer.

When having a thickness of not less than 1 micrometer and not more than1000 micrometers, and an elastic modulus of not less than 1 kPa and notmore than 1 GPa at 30 degrees Celsius, the stretchable resin sheet ofthe present exemplary embodiment can have excellent transferability whenapplied, and hence can easily formed into a resin layer. As a result,the stretchable resin sheet can effectively exhibit the stressrelaxation properties in the above-mentioned applications.

When having the elastic modulus at 30 degrees Celsius of not less than10 kPa and not more than 500 MPa, the stretchable resin sheet canexhibit excellent adhesion, thereby having excellent transferabilitywhen applied, and hence being easily formed into a resin layer withapplying pressure or heat. As a result, in the case of forming thestretchable structure, the stretchable resin sheet can be appropriatelytransferred into between layers or on a layer. In the case that thestretchable resin sheet is in the above-mentioned semi-cured state, theresin sheet can be firmly bonded to an object by applying light or heator by thermal molding, thereby forming a stretchable structure havingexcellent heat resistance, chemical resistance, and stress relaxationproperties.

The stretchable resin sheet formed on the support body can be usedeither together with the support body or alone by being removed from thesupport body. Examples of the stretchable resin sheet used together withthe support body include a flexible substrate and a shield plate wherethe stretchable resin sheet is provided with wires thereon. Examples ofthe stretchable resin sheet used by being removed from the support bodyinclude a heat radiation film and a film provided with wires thereonfabricated by offset printing.

It is preferable that the stretchable resin sheet of the presentexemplary embodiment be a wiring film with a circuit pattern formedthereon. This reduces the stress acting against the external force whichcauses disconnection, exfoliation, or destruction, thereby providinglong-term reliability.

Furthermore, a structure for electronics can be formed by adhesivelybonding or applying a target object, then applying pressure and heat tothe resin composition, the film-like resin composition, or thestretchable resin sheet of the present exemplary embodiment. In thestructure for electronics, the target object is provided between thestretchable resin sheets or on a part or entirety of the surface of thestretchable resin sheet. The structure for electronics may be used as asingle body, or a plurality of the structures may be stacked. In short,this stretchable structure for electronics includes a cured body of theresin composition for stretchable resin sheet and a target object, whichis formed on a part or entirety of the surface of the cured body. In thecase where a plurality of the structures for electronics is stacked, atleast one of target objects included in the structures is disposedbetween the cured bodies of the resin composition of the structure. Sucha structure is preferable because it can reduce warpage and exfoliationdue to stress and can contribute to yield improvement and cost reductionof the electronic devices. Using such a film or structure can achieve aflexible display device that can fit any curved surface and accommodatelarge deformation.

As described above, using the resin composition for stretchable resinsheet of the present exemplary embodiment, a stretchable resin sheetthat has elastic deformability and few residual strains, and also hasstress relaxation properties can be formed.

Using such a stretchable resin sheet can reduce the stress caused bythese deformations, thereby reducing breakage and exfoliation betweencomponents, Which occur in the conventional display devices. Moreover,the stretchable resin sheet of the present exemplary embodiment can berestored to its original shape when released from deformation.

Using such an excellent resin composition for stretchable resin sheetcan achieve a flexible display device or other devices that can fit anycurved surface and accommodate large deformation. Furthermore, havingboth high stress relaxation properties and restoration properties allowsthe resin composition to be applied to various technical fields such asoptical, electronic, adhesive, and medical fields other than as flexibledisplay devices.

It is also preferable that the resin composition for stretchable resinsheet contain epoxy resin and a curing agent. This allows thestretchable resin sheet to be excellent both in stress relaxationproperties and restoration properties, and further to be excellent inheat resistance and toughness.

The present disclosure will now be described in detail by means ofexamples, but, the scope of the present disclosure is not limited tothem.

The examples employ the following materials.

As the polyrotaxane of Component A, SH3400P available from AdvancedSoftmaterials Inc is used. SH3400P contains polyethylene glycol as theaxle molecule, α-cyclodextrin as circular molecules, and an hydroxylgroup as a reaction group.

As the thermosetting resin of Component B, the following epoxy resinsare used: jER1003 available from Mitsubishi Chemical Corporation;EXA-4816 available from DIC corporation; and YP-50 available from NipponSteel & Sumikin. Chemical Co., Ltd. jER1003 is bifunctional and has 7 to8 methyl groups per molecule and a molecular weight of 1300. EXA-4816 isbifunctional and has a large number of methyl groups per molecule and amolecular weight of 824. YP50 is bifunctional and as a large number ofmethyl groups per molecule and a molecular weight of 60,000 to 80,000.

As the curing agent of Component C, a cationic curing agent, SI-150available from Sanshin Chemical Industry Co., Ltd., is used. SI-150 issulfonium antimony hexafluoride. As the imidazole-based curingaccelerator, 2E4MZ available from Shikoku Chemicals Corporation is used.2E4MZ is 2-ethyl-4-methylimidazole.

What is used as the cross-linking agent of Component D is DN-950available from DIC corporation, which is an isocyanate.

As the thermosetting resin of Component E, EP-4003S available from ADEKACorporation, and EG-280 available from Osaka Gas Chemicals Co., Ltd. areused. EP-4003S is a propylene oxide adduct of bisphenol A epoxy resin,and EG-280 is an ethylene oxide adduct of hydroxyphenyl fluorene epoxyresin.

As the curing agent of Component F, the following substances are used:

-   -   a polyfunctional phenolic curing agent (GPH-103 available from        Nippon Kayaku Co., Ltd., which is biphenyl aralkyl phenol);    -   an epoxy resin curing agent (YH-306 available from Mitsubishi        Chemical Corporation, which is an acid anhydride-based curing        agent); and    -   an imidazole-based curing accelerator (2E4MZ available from        Shikoku Chemicals Corporation, which is        2-ethyl-4-methylimidazole).

As other resins, the following substances are used:

-   -   silicone resin (SK-CLEAR sheet available from SK Co., Ltd.);    -   polyethylene resin (UF421 available from Japan Polyethylene        Corporation); and    -   urethane resin (HUX-561 available from ADEKA Corporation).

(Resin Compositions 1 to 8)

Resin compositions 1 to 5 and 8 are prepared by adding the components(parts by weight) shown Tables 2 and 3 to a solvent (methyl ethylketone) in such a manner that the solid content concentration is 40% byweight and by uniformly mixing them (at 300 rpm for 30 minutes). Resigncompositions 6 and 7 are prepared by uniformly mixing the components(parts by weight) shown in Table 3 (at 300 rpm for 30 minutes) in such amanner that the solid content concentration is 100%.

The obtained resin compositions 1 to 5 and 8 are coated on a 75micrometer-thick PET film (support body) using a bar coater, dried at100 degrees Celsius for 10 minutes to remove the solvent, and cured withheat at 170 degrees Celsius for 60 minutes, thereby preparing evaluationsamples of these resin compositions. Meanwhile, the obtained resincompositions 6 and 7 are coated on a 75 micrometer-thick PET film(support body) using a bar coater, and cured with heat at 170 degreesCelsius for 120 minutes in a hermetically sealed condition, therebypreparing evaluation samples of these resin compositions.

(Resin Compositions 9 and 10)

Resin compositions 9 and 10 are already in the form of films, thusdirectly used as evaluation samples.

(Resin Composition 11)

Commercially available urethane resin is coated on a 75 micrometer-thickPET film (support body) using a bar coater and heat-dried at 120 degreesCelsius for 30 minutes, thereby preparing evaluation samples.

The films made of the obtained resin compositions 1 to 11 are used toform stretchable resin sheets each having a thickness of 50 micrometersand a shape of dumbbell No. 6 (the width of the portion to be measuredis 4 mm, and the length of the parallel portion is 25 mm). The resultingstretchable resin sheets are evaluated as follows. Resin compositions 1,2, 3, 6, and 7 correspond to Examples 7-1 to 7-5, respectively, as shownin Tables 2 and 3, whereas resin compositions 4, 5, 8, 9, 10, and 11correspond to Comparative Examples 7-1 to 7-6, respectively.

(Extension-Restoration Test)

In the extension-restoration test conducted in the present exemplaryembodiment, the samples of the Examples and Comparative Examples aresubjected to an extension process and a restoration process under theconditions shown below, and the stress relaxation rate R and theresidual strain rate alpha are calculated by the calculation methodsshown below.

(Extension Process Conditions)

Deflection correction is carried out at a force of not more than 0.05Nin order to eliminate the deflection generated when each test piece isattached to a clamp.

-   -   speed of testing: 25 mm/min from 0% to 25% extension    -   temperature: 23 degrees Celsius    -   extension/holding condition: holding for 5 minutes at 25%        extension

(Restoration Process Conditions)

-   -   Speed of testing: 0.1 mm/min until the tensile force reaches        0±0.05 N    -   temperature: 23 degrees Celsius

The method of calculating the stress relaxation rate: the tensile forceis measured at the time when the extension process is completed, andthis value is defined as initial tensile force F_(AO). Next, after theamount of strain is held under the above extension/holding conditionsfor 5 minutes, the tensile force is measured and defined as F_(A0)(t5).The stress relaxation rate R is calculated by the formula shown below.

$R = {\frac{F_{A\; 0} - {F_{A}\left( {t\; 5} \right)}}{F_{A\; 0}} \times 100}$

The method of calculating the residual strain rate: the amount of strainis measured at the time when the tensile force reaches 0±0.05 N in therestoration process, and this value is defined as the residual strainrate alpha.

The stress relaxation rate R and the residual strain rate alpha obtainedby the above-described method are shown in Tables 2 and 3.

Further, changes in the slope of the tensile force with respect to theamount of strain both during extension and during restoration (the slopeduring restoration/the slope during extension) within the extensionrange of 15 to 20% during the extension-restoration test mentionedabove. The measurement results are also shown in Tables 2 and 3.

(Stress Relaxation Properties Test)

The samples of the Examples and the Comparative Examples mentioned aboveare subjected to an extension process under the conditions shown below,using a tensile-compression tester according to ISO 3384. When theextension process is completed, the tensile force is measured anddefined as initial tensile force F_(B0). After 30 minutes, tensile forceF_(B)(t30) is measured.

(Extension Process Conditions)

Deflection correction is carried out at a force of not more than 0.05Nin order to eliminate the deflection generated when each test piece isattached to a clamp.

-   -   speed of testing: 25 mm/min until reaching 50% extension    -   temperature: 23 degrees Celsius    -   extension/holding condition: holding for 30 minutes at 50%        extension

Next, F_(B)(t30)/F_(B0) is calculated. The calculation results are shownin Tables 2 and 3.

Note that the evaluation samples of resin composition 8 was broken alongthe way, thus is unable to be subjected to either of theextension-restoration test or the stress relaxation properties test.

TABLE 2 Comp. Comp. Example 7-1 Example 7-2 Example 7-3 Example 7-1Example 7-2 resin resin resin resin resin composition 1 composition 2composition 3 composition 4 composition 5 polyrotaxane A1000 100 100 100100 100 thermosetting jER1003 75 150 resin EXA-4816 100 YP-50 100 curingagent 2E4MZ 1.1 1.5 2.25 SI-150 2 additive DN-950 45 45 45 45 45 stressrelaxation rate R 25.3% 43.0% 39.5% 2.0% 82.0% residual strain ratealpha 0.6% 2.7% 1.1% 0.5% 7.3% slope during restoration/ 0.91 0.92 0.831.04 0.98 slope during extension F_(B)(t30)/F_(B0) 0.62 0.6 0.67 0.970.24

TABLE 3 Comp. Comp. Comp. Comp. Example Example Example Example ExampleExample 7-4 7-5 7-3 7-4 7-5 7-6 resin resin resin resin compositioncomposition composition 6 composition 7 composition 8 composition 9composition 10 composition 11 thermosetting propylene 100 — — — — —resin oxide adduct of bisphenol A epoxy resin ethylene oxide — 100 — — —— adduct of hydroxyphenyl fluorene epoxy resin jER1003 — — 100 — — —curing agent GPH-103 49 — 42 — — — YH-306 — 51 — — — — 2E4MZ 0.15 0.150.14 — — — silicone resin SK-CLEAR — — — 100 — — sheet polyethyleneUF421 — — — — 100 resin urethane HUX-561 — — — — — 100 resin stressrelaxation rate R 53.2% 41.1% N/A   1%  31%  35% residual strain ratealpha 2.7% 2.1% N/A 0.1% 8.4% 4.5% slope during restoration/slope 0.830.81 N/A 0.99 58.70 0.87 during extension F_(B)(t30)/F_(B0) 0.41 0.5 N/A0.92 0.75 0.52

(Production of the Structure)

(Mounting a Mirror Wafer with Die Attach Film (DAF) on a Resin Sheet)

An 8″ diameter mirror wafer with DAF (8 mm×8 mm×100 micrometers, DAFlayer: FH900 available from Hitachi Chemical Co., Ltd., which has athickness of 25 micrometers) is applied to each of the resin sheetsformed of resin compositions 1 to 9. These resin sheets are placed on ahot plate heated at 160 degrees Celsius and pressed at 1 MPa for 60minutes, thereby forming specimens of resin sheets with a wafer. Theresin sheet of each specimen is extended by 30% at room temperaturewhile both ends are being held. Next, the extension stress is releasedto confirm the state of the wafer and the adhesion after restoration.The results are shown in Table 4. The evaluation criteria are asfollows.

After being extended, each structure is evaluated as follows: ifrestored without being partially or completely broken, the structure isdetermined to be OK; if not restored although not partially orcompletely broken, the structure is determined to be NG; and ifpartially or completely broken, the structure is determined to be BrokenNG.

Note that Comparative Examples 7-5 and 7-6 are unable to be testedbecause of resin flow due to a high degree of melting of the resinduring heating or during mounting and also because of the largedeformation of the film.

TABLE 4 30% wafer extension/ adhesion restoration Example 7-1 resincomposition 1 OK OK Example 7-2 resin composition 2 OK OK Example 7-3resin composition 3 OK OK Comp. Example 7-1 resin composition 4 OK NGComp. Example 7-2 resin composition 5 OK NG Example 7-4 resincomposition 6 OK OK Example 7-5 resin composition 7 OK OK Comp. Example7-3 resin composition 8 OK Broken NG Comp. Example 7-4 resin composition9 NG Broken NG Comp. Example 7-5 resin composition 10 resin flow — Comp.Example 7-6 resin composition 11 resin flow —

(Mounting a Mirror Wafer Without DAF on a Filler-Containing Resin Sheet)

First, 30 parts by weight of resin solid content of silica (SO-25Ravailable from Admatechs co., Ltd., which has a particle diameter of 0.5micrometers) is added as filler to each of resin compositions 1 and 6.The resulting mixture is stirred for 30 minutes at 3000 rpm using ahomodisper, thereby preparing silica-containing resin compositions.These resin compositions are coated on release-treated PET films using abar coater and heated at 120 degrees Celsius for 5 minutes to remove thesolvent, thereby forming semi-cured films. The semi-cured films areplaced on a hot plate heated at 160 degrees Celsius and heat-treated for60 minutes, thereby forming stretchable resin sheets of Examples 7-6 and7-7.

In the same manner, 30 parts by weight of silica is added to resincomposition 11, and subsequently the same procedure as in Examples 7-6and 7-7 is performed, thereby forming the resin sheet of ComparativeExample 7-7.

In the same manner as in Example 7-1, the extension-restoration test andthe stress relaxation properties test are conducted. Table 5 shows thefollowing values: the stress relaxation rate R, the residual strain ratealpha, the values of the slope during restoration/the slope duringextension, and F_(B)(t30)/F_(B0).

TABLE 5 slope during stress residual restoration/ relaxation strain rateslope during F_(B)(t30)/ rate R alpha extension F_(B0) Example resin39.30% 0.70% 0.9% 0.52% 7-6 composition 1 + silica Example resin 64.10%2.70% 0.82% 0.32% 7-7 composition 6 + silica Comp. resin 45.50% 4.80%0.85% 0.39% Example composition 7-7 11 + silica

The above-described silica-containing resin composition is coated usinga bar coater in the same manner as above and dried at 120 degreesCelsius for 30 minutes, thereby forming a silica-containing resin sheet.A wafer without DAF is placed on each of these resin sheets and pressedat 160 degrees Celsius and 1 MPa for 60 minutes, thereby forming resinsheet specimens having a wafer. The resin sheet of each specimen isextended by 30% at room temperature while both ends are being held inthe same manner as in Example 7-1. Next, the extension stress isreleased to confirm the state of the wafer and the adhesion afterrestoration. The results are shown in Table 6. Note that in ComparativeExample 7-7, the wafer is buried because of resin flow due to a highdegree of melting of the resin.

TABLE 6 30% wafer extension/ adhesion restoration Example 7-6 resincomposition OK OK 1 + silica Example 7-7 resin composition OK OK 6 +silica Comp. resin composition resin flow — Example 7-7 11 + silica

The aforementioned results indicate that the stretchable resin sheet ofthe present exemplary embodiment can be restored to its original statewithout damage after being extended.

The cured material of the resin composition for stretchable resin sheetof the present exemplary embodiment can exhibit excellent restorationproperties after extension and stress relaxation properties even if itcontains inorganic filler.

These facts indicate that the stretchable structure of the presentexemplary embodiment is useful as various electronics elements.

The sheet-shaped stretchable structure of the present disclosure has ahollow, which satisfy not only mountability and sealing properties butalso extensibility, allowing the structure to be flexible and pliable.In addition, using this structure can achieve flexible display devices,flexible electronic circuits, etc. that can fit any curved surface andaccommodate large deformation.

Furthermore, having not only high stretchability but also mountabilityand sealing properties allows the structure to be applied to varioustechnical fields such as optical, electronic, adhesive, and medicalfields other than as flexible display devices. Hence, the structure isindustrially very applicable.

The resin composition for stretchable resin sheet of the presentdisclosure is also useful as various electronics elements.

What is claimed is:
 1. A sheet-shaped stretchable structure, comprising:stretchable resin sheets laminated together, and a conductive layerdisposed at one of following positions: between any two adjacent ones ofthe laminated stretchable resin sheets; on a top surface of an uppermostone of the laminated stretchable resin sheets; and on a bottom surfaceof a lowermost one of the laminated stretchable resin sheets, and a viahole.
 2. The sheet-shaped stretchable structure according to claim 1,wherein the conductive layer is a copper foil.
 3. The sheet-shapedstretchable structure according to claim 1, wherein the via is formed bylaser-drilling.
 4. The sheet-shaped stretchable structure according toclaim 1, wherein the laminated stretchable resin sheets comprisesrubber.
 5. The sheet-shaped stretchable structure according to claim 4,wherein the laminated stretchable resin sheets comprising the rubber iscured or semi-cured.
 6. A flexible display device containing thesheet-shaped stretchable structure according to claim 1.